Robert Knepper ("Prison Break")
He's known as T-Bag, but Robert Knepper is anything but watered down. He does the crazy psycho guy, and the sympathetic schlub, somehow simultaneously. While being reminiscent of Robert De Niro in "Cape Fear," Knepper has still made the character very much his own -- and revelations about his own backstory of sexual abuse have made him a remarkably sensitive character. In particular, T-Bag's flashback scenes with his girlfriend have a tenderness to them that make Knepper much more than a jail-yard bogeyman. We wouldn't mind seeing another 5-to-10 sentence with this guy.
And that's why I love T-Bag. Even if he is a murdering s.o.b. :o)
Other people who made the list:
Creed Bratton from The Office, Jack Coleman from Heroes and Michael Emerson from Lost. And they're all favorites of mine.