Yay dubious smiley!
That’s funny, I always confuse James Coburn with Jason Robards. Does anyone mistake Robards for Marvin? Probably not.
The big mother or all confusing pairs for me, though, is Jeff Daniels and Bill Pullman. I really think they are the same person.
I can’t believe Dante beat me to the Daniels/Pullman match because I stopped to read the IMDB entry for Arachnaphobia. I couldn’t remember which one was in it.
Burt Reynolds and Tom Selleck. Too many mustaches to go around.
And call me crazy, but I used to think Ben Affelek was Adam Sandler.
The guy who played the near-deserter private from Brooklyn (one of the 2 or 3 who survived) in “Saving Private Ryan” and Ben Affleck.
When I saw it in the theater, I thought it was Affleck. The first thing I thought was, that’s a pretty good performance for Ben Affleck. The second thing I thought was, I guess Matt Damon really is his butt-buddy.
Mary Kate and Ashley Olsen…never could tell those two apart. 
I used to mix up John Stewart and Jon Cryer.
I never physically mixed them up, but I still have trouble remembering which one is Ben Stiller and which one is Jerry Stiller. I also don’t know which one is Hall and which one is Oates even though I can definitely tell them apart.
Others…
Merle Haggard and Waylon Jennings
Gary Busey and Nick Nolte
FriarTed, do you mean Kathy Griffin (from Suddenly Susan) and Vicki Lewis (from NewsRadio)?
I mix up the Baldwins and the Daniels often.
Kate Hudson and Kirsten Dunst. I know what the look like, but I can’t ever remember their names. I’m always calling one the other name.
Dennis & Randy Quaid. Although they play very different roles and I can normally tell them apart on sight, I tend to confuse the two when trying to remember which is which.
Don Cheadle, Courtney B. Vance and another guy (now I’ve drawn a blank one his name).
I always mix the three of them up.
I watched the entire movie thinking it was Affleck.
Another one is Kirk Douglas and Lloyd Bridges. I saw the Seinfeld episodewhere Bridges was on there and I kept thinking “Didn’t he have a stroke? He’s doing pretty well” until realizing it was Bridges.
Also, Tom Sizemore and Michael Madsen.
Wow. Missed it by 10 minutes. This is exactly what I was going to say. I saw a Tom Sizemore movie a couple of years ago and remember telling the people I was with “That’s Mr. Blonde from Reservoir Dogs” but nobody would listen. Silly me.
Jeff Bridges and Dennis Quaid are one and the same in my mind, and Kevin Costner is 85% their triplet.
Lloyd Bridges and Leslie Neilsen, similar names and they both did madcap roles in slapstick comedies recently.
It took a long time for me to be convinced that Julia Stiles and Erika Christensen aren’t the same person. I used to have that confusion around Reese Witherspoon and Alicia Silverstone, but Alicia Silverstone has sort of vanished.
For some reason I always used to confuse Brad Pitt and Johnny Depp. I’ve gotten over that.
And of course one Baldwin is pretty much the same as the next one.
Jeff Daniels and Dave Coulier always confuse me.
I loved the scene in GANGS OF NEW YORK where Reilly and Brett Somers finally make love.
I confuse Skeet Ulrich and Johnny Depp in late night movies. There’s also an actor who has the misfortune of looking just like Dick Cavett who’s in several things.
Ben kingsly and f murry abraham, Kingsly played Ghandi and abraham played the dude who killed mozart in Amedeus. I went my whole life thinking they were the same guy untill like a year ago.
Huh. The individuals for my biggest mixup have been mentioned, but not together: Jeff Daniels and Jeff Bridges. I can never remember which is which.
Hi all, first time poster here.
The two actors I get confused are Chris Tucker and Chris Rock. I mean, I can tell them apart, but I think, “The one in the Fifth Element was… Tucker. No, Rock! No, Tucker!”
Jennifer Beals and Debra Winger.
Kevin Pollack and Kevin Spacey.
Well, these aren’t individual people, but Journey and Foreigner will get me every time.