already mentioned:

daniel day lewis in THERE WILL BE BLOODE and GANGS OF NEW YORK.
tupac in JUICE


NOT mentioned yet:

EVERYONE in THE DEPARTED
Robert De Niro's assassin as Al Capone in the movie UNTOUCABLE(guy that wears all white)
Jet Li in FEARLESS
Maggie Q in the last DIE HARD movie
Mel Gibson in the PATRIOTS
guy in 28 WEEKS LATER(guy who left his wife to die)

thats all i can think of now.