He was OK, but he was no Gene Kelly. 
Yes, but she was in Bullets Over Broadway, which is one of Woody Allen’s better movies, and she had some hot, steamy lesbian scenes with Gina Gershon in Bound, the Wachowski Brothers’ first movie, which isn’t bad as a neo-noir film either.
Gene Kelly? Too butch – too intent on proving “I may be a dancer, but I’m no poofter.” Fred was secure enough in his masculinity not to need to make a point of it.
Also – in terms of straight technique – gotta give it to Fred. After all, which of the two is Baryshnikov’s idol?
I’ll go with Melanie Griffith. Who was the wiseass who put her on stage in Chicago? And hubby Antonio Banderas is a lower-rate Arnold.
Arnold does have some insight into his “talent.” When asked how to make it big, he replied: Three things. Study hard, work hard, and marry a Kennedy. I like a person who can laugh at himself.
WHAT WHAT WHAT?
So he plays off-key people. Other than that, his characters don’t have a hell of a lot in common. People cast him as strange characters because he’s such a good actor that he can nail any role convincingly, no matter how hard it would be to take seriously. See: As Good As It Gets, About Schmidt. I defer you to name any actor who could pin down all the strange and varied roles that Nicholson has, as well as he has.
Network News has a Five Easy Pieces moment? Chinatown? The Last Detail?
I’d consider Al Pacino, Gary Cooper, Clark Gable, Sean Connery, Spencer Tracy, Randolph Scott, among others for Johnny-One-Note (or most resourceful if you follow the OP’s logic) before Nicholson. Adam Sandler springs to mind also, but I couldn’t bear to use his name in the same sentence with those other guys.
You forgot Eddie Murphy.
I second the votes for Hanks and Nicholson. Hell, I didn’t think they were the talented ones in “Bosom Buddies” and “Easy Rider” and that’s comparing them with Peter Scolari and Dennis Hopper, ferchrissake.
Not really a movie star but perhaps the luckiest no-talent around has to be Ringo Starr, but he seems to know it.