In no real order:
Tom Hardy - Surprised only a couple of people have mentioned him, such a diverse and talented actor
Marlon Brando
Ryan Gosling - After watching drive, he is one of my favourite actors, best film of last year imo
Morgan Freeman
Tom Hanks
Heath ledger
George Clooney
Robert Di Niro
Adrian Brody
Robert Downey Jr.
This list is just off the top of my head, I have so many favourite actors as they all play such different roles in films.
(CBA to write about them after the 3rd :P)