Definitely some joke picks in here. I have to go Hackman (don't forget Bonnie and Clyde, Birdcage, Hoosiers, French Connection, The Conversation, Crimson Tide among all of the movies that immediately come to mind).
A guy who hasn't been mentioned is Woody Harrelson who mirrors his Cheers persona in Doc Holliday and Wag the Dog to being outfront as Larry Flynt, in Kingpin (a top five all time comedy), and as evil in Natural Born Killers. Throw in White Men Can't Jump and No Country for Old Men if you are looking for range.