Just going off Locke's post in the last film he watched thread, a couple sprung to mind:
John C Reilly - We Need to Talk About Kevin. Just a bit of a shock really to see the guy from Step Brothers and Dewey Cox playing a husband and father who's
Jim Carrey - Eternal Sunshine of the Spotless Mind, The Truman Show. A little unfair to write him off as that wacky Mask/Ace Ventura dude, because he's capable of playing excellent, 3D and complex characters.
I understand Jonah Hill is amazing in Moneyball but I haven't seen that yet.