Current:
Jacobs Field (or whatever they call it now.)
Fenway Park
Anaheim Stadium
US Cellular Field
Comerica Park
PNC Park
Wrigley Field
Oriole Park at Camden Yards
Past
Cleveland Municipal Stadium
Tiger Stadium
Comiskey Park
Yankee Stadium II
Shea Stadium
Riverfront Stadium
3 Rivers Stadium
Milwaukee County Stadium
Exhibition Stadium
Baltimore Memorial Stadium
Montreal Olympic Stadium
Hiram Bithorn Stadium in San Juan PR, to see the SF Giants play Montreal
I’m possibly the only poster to have seen games in the old Griffith Stadium on Florida avenue in DC.
I feel so inadequate…my list very short…
Candlestick Park
Oakland-Alameda Coliseum (before they renamed it O.co part, or whatever it is these days)
Phone Company (aka Pac Bell/SBC/AT&T) Park
Technically I’ve been to Fenway as well, but only for a stadium tour, not for a game.
Current:
Rogers Centre (Blue Jays)
Ballpark at Arlington (Ranger)
Past:
Metrodome (Twins)
Metropolitan Stadium (Twins)
ETA: Had my picture taken at Wrigley but the Cubs were on the road when I was there.
Current:
Jacob’s Field
Nationals Park
Fenway Park
Wrigley Field
Defunct:
Cleveland Municipal (“The Mistake by the Lake”).
Current (23): CHW, MIN, DET, KC, CLE, NYY, BOS, BAL, TOR, OAK, TEX, CHC, STL, MIL, PIT, HOU, CIN, ARI, SF, COL, NYM, WAS, ATL
Former (11): CHW (Comiskey), MIN (Metrodome), DET (Tiger Stadium), NYY (old Yankee Stadium), BAL (Memorial), SEA (Kingdome), STL (Busch), MIL (Milwaukee County), CIN (Riverfront), NYM (Shea), ATL (Fulton County)
Current:
Seattle
Oakland
San Francisco
Los Angeles
Anaheim
Colorado
Texas
Kansas City
Minnesota
Milwaukee
Chicago (both)
Detroit
Toronto
Cleveland
Cincinnati
Atlanta
Baltimore
Pittsburgh
Boston
Past:
Kingdome
Jack Murphy Stadium
Busch Stadium
Metrodome
County Stadium
Tiger Stadium
Veterans Stadium
Shea Stadium
Yankee Stadium
Golly. Some impressive lists.
Current:
Nationals Park (D.C.)
Camden Yards (Baltimore)
Dodger Stadium (L.A.)
Former:
RFK Stadium (D.C., many Nats games, also some soccer games)
Municipal/Lakefront Stadium (Cleveland, for both Tribe and Browns games)
Riverfront Stadium (Cincy)
Busch Stadium (the second one)
Oh, I also went on a tour of Enron Field (now Minute Maid Park) years ago but I never saw a game there.
–Cliffy
Former:
Yankee Stadium
I’ve only seen one baseball game in my life. But I’m from Europe, so that’s still more than most people I know.
Current:
None
Past:
Jack Murphy
Mile High before Coors Field was built
I like baseball, went to an awful lot of minor-league games as a kid, but somehow have never made it to more than two MLB games in my life.
For baseball games, present:
Citi Field
New Yankee Stadium
Kauffman Stadium
Oriole Park at Camden Yards
Past:
Old Yankee Stadium
Shea Stadium
visited without a game:
Olympic Stadium
Skydome
Fenway Park
I’ve only been to the Kingdome and Safeco Field in Seattle.
Current stadiums (stadia?):
The current Busch Stadium, St. Louis
Miller Park, Milwaukee
Wrigley Field, Chicago
Kauffman Stadium, Kansas City
Yankee Stadium, New York (although for a football game, last December’s Pinstripe Bowl)
No longer in use for baseball:
The previous Busch Stadium, St. Louis
Metrodome, Minneapolis
I was very impressed by Yankee Stadium. I wasn’t sure what to expect, but that’s a fine fan experience (even with the moat and the alligators between the general public and the field-side seats). Old Busch was also a far, far better place for baseball than it had a right to be - since it was one of the 1970s all-purpose round stadiums, I thought it might not be optimized for baseball, but it was great. The New Busch, of course, is fantastic.
On the other side, Wrigley is historic and picturesque and all, but it’s cramped, uncomfortable, has plenty of seats with lousy sightlines, and you feel like a rat in a maze trying to find your seat in there. But it’s still a baseball palace compared to the Metrodome. I imagine that’s a fun place to watch football in, but it was a shame Twins fans had to deal with that. Talk about a stadium designed around football that they crammed baseball into, that’s the Hump. I would love to get a chance to take a trip and see the Twins in their new (outdoor) digs someday soon.
Wrigley Field
Tiger Stadium
I did this in another thread and have some updates:
9 - Pacific Bell Park, San Francisco Giants (or whatever its current corporate name is.) Fantastic stadium in every respect; beautiful location, lovely ballpark, kid-friendly, great walk-around value, and you have to adore the garlic fries. Does get very cold at night.
8 - Petco Park, San Diego Padres. As nice as you’ve heard.
7 - Comerica Park, Detroit Tigers. Very lovely park, and one thing I like about it is they took the idea of a park being built primarily for a particular team and really ran with it. Major disadvantage: it’s in Detroit.
7 - Turner Field, Atlanta Braves. A shockingly nice park; you would never, ever know it was once an Olympic coliseum. Has a Braves Hall of Fame, which is a great idea not used many other places. Easy to get good seats and a lovely park. Loses points for there being nothing of interest around it.
7- Wrigley Field, Chicago. Every bit as charming as you’ve been told.
6 - Rogers Centre, Toronto Blue Jays. Significantly improved over the last five years due to a concerted refurbishment effort; would have earned a 4 in 2004. Still too much concrete and astroturf and not enough good food, but unique, great sightlines, and unquestionably the best LOCATED stadium in all of baseball.
6- Cellular Field, Chicago White Sox. Not as bad as I had been led to believe. Good looking park, good food, nice area in center field. Reasonably priced. Loses two points for being in the damned ghetto.
6 - Bank One Ballpark, Or Whatever It Is Now, Arizona Diamondbacks - A modern park with nice amenities, but a bit too vertical in construction and the structure of the outfield looks stupid in person. Well located.
5 - Fenway Park, Boston. A lot of points for history and an enthusiastic crowd; not actually a comfortable park, though. Very expensive and the food was surprisingly bad, though maybe my expectations were too high. Definitely not Wrigley.
5 - Angels Stadium - Serviceable. Accessibly only by car, so far as I can tell. Not ugly, nice walkaround, but nothing special. Very good, enthusiastic fans, which I did not expect.
5 - Miller Park, Milwaukee. Serviceable. Actually, it’s above average inside, but very, very poorly located and getting from your car to the stadium is only a slightly shorter walk than if I’d just started walking from my house in Ontario.
5 - Old Yankee Stadium, New York Yankees. For all its glory and history it was in a lousy neighborhood and the place looked its age.
4 - Exhibition Stadium, Toronto - One of the more ill advised ballparks in recent baseball history, but ranks above the really bad ones by virtue of a very nice location, a good crowd, and being sort of goofy and charming.
3 - Shea Stadium, New York Mets - Bleah. Nothing, really, was good about this park.
2 - Whatevertheycallit Coliseum, Oakland. Hideous ballpark, terrible food, located nowhere.
0 - Stade Olympique, Montreal Expos - Hideous. An absolute dungheap and an embarassment to Major League Baseball. It was painful to attend games in this gigantic pile of merde.
Wrigley Field - This is baseball. The food needs a lot of help and the prices have gotten crazy, but it’s still the best experience in baseball. I loathe all the gimmicky promos and blaring music and jumbotron antics in new parks, so distracting and makes me feel like I paid to watch commercials. Wrigley gets tons of point for not having that.
Old Comiskey Park - I hate the Sox, but this was my home park as a kid growing up in the southwest burbs. It was old and beat up, it was in a terrible neighborhood, it had more obstructed view seating than unobstructed. But, it got really loud and had a great blue collar city vibe. Felt like you went back in time, moreso than Wrigley because of it’s grit.
New Comiskey Park - It’s the last of the giant, soulless concrete bowls. The upper deck is a adventure in vertigo. Built at precisely the wrong time, before people realized that ballpark character was worth something. Now the Sox are probably stuck with it for another 50 years. The food was a big improvement, but it’s still in the ghetto.
New Comiskey Park v2.0 - Basically the same park as above, but the Sox realized the error of their ways. Knowing they were stuck with the place for a long time the endeavoured on a $100M+ remodel that changed just about everything but the concrete. The result is a much friendlier stadium with a lot more amenities and charm. It’s still never going to become a landmark like Camden, Tigers and PNC Parks but it’s at least livable. Still has a crazy upper deck and that ghetto.
Miller Park - I like to think of it as Wrigley North, not because it shares any of it’s charms but because it houses almost as many Cubs fans for 8-10 games a year. Never made it to old County Stadium but by all accounts this is a huge improvement. The location kinda sucks, it’s easy to drive to but it lives in the middle of a cloverleaf, so the charm factor is pretty much nil. The food is solid, and the sightlines are good. It’s infected with a insane amount of marketing, gimmicks and distractions from baseball though. The best part about Miller Park is the NFL style tailgating that occurs every game, never seen that at a baseball game before.
Old Busch Stadium - A steaming, festering pile of shit in every way. And not just because of all the Cardinals fans. Remember those negative comments about soulless concrete bowls? This is the poster child and the Sox should be embarrassed that they didn’t learn a better lesson. This place has shitty sight lines and felt like it was on the surface of the sun. Mid-summer in St. Louis is already hot, Busch stadium was a giant concrete bowl sunk 10 feet into the ground and lined with asphalt and astroturf without a lick of shade, all things that amped up the heat to about 145 on the field. Plus the food sucked, the only redeeming quality is that it was right downtown next to the Arch. Downtown St. Louis is pretty enough to look at, but no one lives there, it’s pretty much deserted when there’s no game. It does have the Landing, Soulard and the vice over in East St. Louis, but charm isn’t really part of the equation.
New Busch Stadium - Pretty much exactly the same as the old one, except with better sight lines, real grass, brick and all the distractions I mentioned about Miller Park. The food is so-so, except the gourmet nacho bar, that’s good stuff.
New Yankee Stadium - It’s really big. It’s in a really shitty neighborhood. The new park distractions aren’t as bad as Miller or Busch, but it’s still a new park looking to sell you anything and everything except baseball, beer and food. At least it’s not treated like a kiddie playground and most of the people are there for baseball, not daycare. It’s really attractive, I’ll give it that, and the concourses are wide and easy to get around. Supposedly the bleachers suck, I had great seats by thee dugout so I was plenty happy with the views. The prices here couldn’t be more insulting, making all that advertising and in-between inning shilling doubly bad.
Fenway Park - I guess it could be that I’m just too much of a Wrigley honk to see it, but I don’t get the appeal here. The park is old but not in a particularly charming way, more like old Comiskey than Wrigley. The sight lines are utterly atrocious and the seats are torture devices. The food sucks and the prices are a kick in the nuts. The crowd is great and the atmosphere pre- and post-game is great, better than Yankee Stadium, I’ll give it that and the neighborhood has gotten pretty fun. It’s still sort of in the middle of a warehouse district unlike the residential neighborhood of Wrigley, but enough of those places have converted to trendy bars and lofts to make it enjoyable.
PacBell Park - Really nice stadium in an amazing location. I was there as a tourist by myself and took in a game with my friend. Seeing PacBell was like seeing a tourist attraction, so I count that as a major win for a new park. Being right on the bay and walking around the place makes for a terrific afternoon. The food is really good, though it’s pretty tough to get over the fact that it doesn’t remotely resemble ballpark food, but tasty none-the-less. My biggest issue here was with the lackadaisical nature of the fanbase. Everyone is there late, leaves early and treats it like a picnic in the park. That’s fine I guess, and I suppose people might similarly bash Wrigley for being a giant beergarden, but for me the wine and cheese crowd is a little off-putting.
Current, NL:
[ul]
[li]AT&T Park (Giants)[/li][li]Coors Field (Rockies, for the 2007 World Series!)[/li][li]Dodgers Stadium (Duck the Fodgers! :D)[/li][li]PNC Park (Pirates)[/li][li]Petco Park (Padres)[/li][li]Busch Stadium (Cardinals)[/li][/ul]
Current, AL:
[ul]
[li]Oriole Park[/li][li]Fenway Park (Red Sox)[/li][li]US Cellular Field (White Sox)[/li][li]Progressive Field (Indians)[/li][li]Comerica Park (Tigers)[/li][li]The Coliseum (A’s)[/li][li]Tropicana Field (Rays)[/li][li]Ameriquest Field (Rangers)[/li][li]Rogers Centre (Blue Jays)[/li][/ul]
Past, NL:
[ul]
[li]Candlestick Park (Giants)[/li][li]Shea Stadium (Mets)[/li][li]Astrodome (Astros)[/li][li]Jack Murphy Stadium (Padres)[/li][/ul]
Past, AL:
[ul]
[li]Angels Stadium[/li][li]Yankee Stadium[/li][/ul]
Teams I have not yet seen at their home park:
[ul]
[li]AZ Diamondbacks[/li][li]Atl Braves[/li][li]Chi Cubs (they were on the road when I was in Chicago; I toured Wrigley, though)[/li][li]Cin Reds[/li][li]Mia Marlins[/li][li]Mil Brewers[/li][li]Phi Phillies[/li][li]Wash Nationals[/li][li]KC Royals (will be there in 3 weeks!)[/li][li]MN Twins[/li][li]Sea Mariners[/li][/ul]
New parks I have not yet been to:
[ul]
[li]Citi Field (Mets)[/li][li]Minute Maid Park (Astros)[/li][li]Angels Stadium (since the redesign after the Rams left)[/li][li]New Yankee Stadium[/li][/ul]
Current:
All of them except the new Miami Marlins stadium (Hope to get there next year!)
Past:
Memorial Stadium (Orioles)
Old Yankee Stadium (Yankees)
Old Comiskey Park (White Sox)
Cleveland Municipal Stadium (Indians)
Tiger Stadium (Tigers)
HHH Metrodome (Twins)
Kingdome (Mariners)
Arlington Stadium (Rangers)
Fulton County Stadium (Braves)
Pro Player Stadium (Marlins)
Shea Stadium (Mets)
Veterans Stadium (Phillies)
Olympic Stadium (Expos)
Riverfront Stadium (Reds)
Astrodome (Astros)
County Stadium (Brewers)
3 Rivers Stadium (Pirates)
Old Busch Stadium (Cardinals)
Jack Murphy Stadium (San Diego)
Candlestick Park (Giants)
…For a grand total of 49. I’ll be impressed if anybody here can beat that. 
In 1993 I saw a ballgame in every major league ballpark. There were 28 at the time. Many of the ones I visited have been replaced, and the only new ones I’ve seen since then are AT&T Park in San Francisco and Rangers Ballpark in Arlington.
The ones I’ve been to are:
Oakland Coliseum (now officially called O.co Coliseum) (A’s)
Candlestick Park (Giants)
AT&T Park (Giants)
Dodger Stadium
Mile High Stadium (Rockies)
Yankee Stadium (the old one)
Atlanta-Fulton County Stadium (Braves)
Rogers Centre (then known as the Sky Dome) (Blue Jays)
Arlington Stadium (Rangers)
Rangers Ballpark in Arlington
Seattle Kingdome (Mariners)
Camden Yards (Orioles)
Angel Stadium (The Big A)
Busch Stadium (the old one)
Veterans Stadium (Phillies)
Lakefront Stadium (Indians)
Jack Murphy Stadium (AKA Qualcomm Stadium, Padres)
Riverfront Stadium (Reds)
Shea Stadium (Mets)
Milwaukee County Stadium (Brewers)
Tiger Stadium
Wrigley Field (Cubs)
Astrodome (Houston)
U.S. Cellular Field (White Sox, then known as New Comiskey Park)
Metrodome (Twins)
Three Rivers Stadium (Pirates)
Kaufmann Stadium (Royals)
Fenway Park (Red Sox)
Joe Robbie Stadium (Marlins)
Olympic Stadium (Montreal Expos)
That makes 30.
Current:
Safeco in Seattle.
Citi (I think its called). Game ended on an unassisted triple play, happened only once before.
Wrigley Field.
Fenway Park.
Sky Dome.
Past:
Shibe Park/Connie Mack. Grew up in Philly and saw many games there.
Shea. Only game I saw there was a perfect game. First one after Don Larsen.
Jack Murphy.
Cleveland Muni.
Briggs Stadium.
Jarry Park.
Olympic Stadium.
Kingdome.