Tiger Stadium, Detroit. Many times.
Comerica Park, Detroit. Twice so far.
Busch Stadium II (the one before the current one), St. Louis. Once.
Bank One Ballpark (then the name of it), Phoenix. Once.
This year, God willing, I will add Yankee Stadium to the list and perhaps in the next decade add a few more.
Fenway Park (50+ times)
Yankee Stadium (3 times)
Mile High Staduim (Rockies)
Camden Yards
Stade Olympique (Montreal) (10+ times)
Good times, good times…
Shea Stadium - NYM
Yankee Stadium - NYY
Veterans Stadium (defunct) - PHI
Citizen’s Bank Ballpark - PHI
Fenway Park
Turner Field
RFK Stadium (defunct) - WAS
Olympic Stadium (defunct) - MON
PNC Park - PIT
Miller Field - MIL
Wrigley Field - CHC
Busch Stadium - STL
Kaufman Stadium - KC
The Great American Ballpark - CIN
US Cellular Field (?) - CHW
So that’s 15, which isn’t bad. I’m hoping to get to Baltimore and the new stadium in DC later this summer, and maybe also Toronto if I can get up the werewithal for a longer road trip.
The Astrodome
Whatever they’re calling Enron/Minute Maid now
Arlington Stadium
Whatever they’re calling the Ballpark at Arlington now
Old Busch Stadium
Fenway Park (but not on game day 
)
Whatever they’re calling Bank One Ballpark now
Tiniest little list yet:
Turner Field
[del]Joe Robbie[/del] [del]Pro Player[/del] Dolphin Stadium
PNC Park
For games:
Yankee Stadium
Shea Stadium
Kauffman Stadium
Oriole Park at Camden Yards
For non-game tours:
Olympic Stadium
Skydome (before it was re-named Rogers Centre)
I’ve probably seen homes of a majority of MLB teams from the outside, though. Most of my children’s usable vacation time comes during the winter. I know I’ve seen Anaheim, Network Associates (was right next to it, to see a Warriors game in the Oakland Arena), Pac Bell, old Busch (looking down on it from the Arch), Turner, RFK, Jacobs, Great American, Fenway, Kingdome and the then-still-under-construction Safeco (from atop the Space Needle), Metrodome (as well as the marker for old Metropolitan Stadium’s home plate in the middle of the Mall of America), PNC, Veteran’s Stadium, Citizen’s Bank and Comerica.
Riverfront Stadium (Reds; superseded)
Three Rivers Stadium (Pirates; superseded)
Veterans Stadium (Phillies; is it still there?)
Kingdome (Mariners; superseded)
Wrigley Field
Fenway Park
Moving thread from IMHO to Game Room.
Metropolitan Stadium
Metrodome
Yankee Stadium
Shea Stadium
Fenway Park
Old Comiskey Park
Wrigley Field
Dodger Stadium
Angels Stadium
The Ballpark at Arlington (TX)
Old Veteran’s Stadium (Philadelphia)
Petco Park (SD)
Camden Yards
Fulton County Stadium
Dolphins Stadium (Marlins)
The Ballpark in Arlington (Rangers)
Oakland Coliseum
Dodger Stadium
Angels (both before the Edison Field renonavations and after)
Dolphin Stadium
No longer in use:
Candlestick
Qualcomm
Astrodome
With numbers of games:
Joe Robbie Stadium (about 1000 games the last 15 years)
Riverfront Stadium (about 5)
Veterans Stadium (2 or 3)
old Busch Stadium (1)
Tiger Stadium (1)
Wrigley Field (1)
old Comiskey Park (1)
Baltimore Memorial Stadium (2)
Camden Yards (1)
Arlington Stadium (1)
Shea Stadium (1)
Tropicana Field (Tampa) (1)
Jack Murphy Stadium (San Diego) (1)
I’ve only ever been to Shea Stadium, Yankee Stadium, Oriole Park at Camden Yards and Wrigley Field for baseball games.
I’ve been to Fenway and The Big O (Olympic Stadium, or Stade Olympique) in Montreal when the Expos played there, but in the offseason, which maybe doesn’t really count.
Anytime I’m TDY I try to get to an away stadium/arena if possible. Also roadtrips for the specific purpose of seeing stadia:
Memorial Park
Camden Yards
The Vet
Yankee Stadium
Fenway
The Trop
Comiskey
Wrigley (pissed we didn’t drive up to Milwaukee while in Chicago)
The Jake
Tiger Stadium (but not Comerica)
Arlington
Edison
Doger Stadium
Kingdome (but not SafeCo)
The Coliseum
AT&T Park (but not Candlestick)
The Murph (but not Qualcomm)
Turner Field
Good topic:
Cleveland Stadium
Jacobs Field aka whatever insurance company owns the naming rights now field
Tiger Stadium
Comerica Park
Old Comiskey Park
New Comiskey Park
Wrigley Field
Milwaukee County Stadium
Toronto Exposition Stadium
3 Rivers Stadium
PNC Park
Riverfront Stadium
Angels Stadium
Royals Stadium
Yankee Stadium
Fenway Park
Shea Stadium
Montreal Olympic Stadium
Camden Yards
Baltimore Memorial Stadium
plus I saw the Giants play the Expos in San Juan PR when they played there in 2004.
Thanks for sharing folks! The thing about my list - I grew up in St. Louis w/ season tix, so old Busch is the lion’s share for me. Went to school in Dallas, so there’s those. Moved to SF, so there’s those parks. And I have brothers / friends living in Chicago, Houston, San Diego, and western Mass. So not that difficult when you think about it.
I never have been to NYC (other than airports and stuff) so I really should do that. Do you think I could squeeze in Camden Yards if I visited NYC or is that too unmanageable?
Funny you should mention George Brett - I was at the last game at Arlington Stadium, which was also George Brett’s last game. At his last at-bat, Bobby V had Tom Henke pitch him nothing but fastballs since he so far had been hitless. He hit one up the middle that Manny Lee should’ve gotten to, but he eased up so Brett could get the base hit. During the at-bat all the Rangers were standing in the dugout and Nolan Ryan (also his last game) tipped his cap. Pretty cool.
I have never been to the Metrodome, but I have a hard time believing that it is worse than Tropicana Field in Tampa Bay. That was the most depressing stadium I’ve ever been to in my life, not only because of the structure of the place but because of the atmosphere within it. I went to a Red Sox/D-Rays about 8 years ago and there might have been 100 Ray fans in the place. If that.
Also, there is no way that the Coliseum–an outdoor park–can be worse than Tampa.
My list (short) list:
Veteran’s Stadium
Citizen Bank Park
Camden Yards
Yankee Stadium
Fenway Park
Anaheim Stadium
Tropicana Field
Morbo:
Baltimore is, with good traffic, a 4 hour drive from New York City. I’d recommend waiting for an occasion to be flying to Washington DC to detour to Camden Yards rather than trying to squeeze it into a New York trip.
If you’re in New York and want to see MLB stadiums other than the Yankees and Mets, Philadelphia is closer by, and Boston is about the same distance from NYC as Baltimore is, but with fewer tolls to pay (on the other hand, the trip to Baltimore allows you to buy gas cheaply in NJ).
Chronological order:
Milwaukee County Stadium
Wrigley Field
Fulton County Stadium
Candlestick Park
Bank One Ballpark (Arizona)
Pacific Bell Park
New Comiskey
Miller Park
Turner Field
Oakland Coliseum
Favorite: PacBell. About as perfect as any ballpark experience can be. Sorry Wrigley.
Least Memorable: Fulton County Stadium (I’d hardly remember it at all if not for the creepy guy masturbating at the urinal trough…ugh.)
Most Vertigo Inducing: New Comiskey…the upper deck really should be rated for mountaineers only
Most Nostalgic Memory: Seeing Andre Dawson homer at Wrigley during the otherwise disasterous '87 season.
Wow. I really need to brush up on my East coast geography. 
I have been to Fenway, so I guess if my NYC trip happens I’ll concentrate on getting to Philly and schedule Camden yards for another trip. My oldest brother just moved to the DC area so that’ll get done sooner or later.