Kevin spacey- American beauty Ellen burstyn- Requiem for a dream Edward norton- American history X/ 25th hour Meryl streep- Sophies choice Johnny depp- Edward scissorhanRAB/ Ed wood / Pirates of the caribbean Hilary Swank- Boys dont cry/ Million dollar baby Dustin hoffman- Midnight cowboy/ Rain man Eileen walsh- The magdalene sisters Brad davis and john hurt- Midnight express Charlize theron- Monster
I'd have to think to come up with older ones, and so many films were driven by sole/dual characters back then, that there were many great individual performances. Mitchum is a great shout.
Recently:
Hilary Swank - Boys Don't Cry
Jason Schwartzman - I Heart Huckabees
Choi Min-sik - Oldboy
Paddy Considine - Dead Man's Shoes
Cameron Bright - Birth (for his age alone. The film sucks but he out acts any kid i've seen before, and the credit Haley Joel Osmond got for his p1ss poor performances makes this kid a genius)
Although its not my favourite film and he's not my favourite actor (he's done too many crap films), is in the top 30 though . Rutger Hauer in Blade Runner.
Another two that spring to mind
James Stewart in Harvey
Alec Guiness in the Ladykillers
Patricia Arquette in True Romance
Edward Norton in American History X
Natalie Portman in Leon
Johnny Depp in Pirates of the Caribbean
Michael Clarke Duncan in The Green Mile