I'm 60 and have been a film-goer all my life - these are my favorite performances.
In no particular order...
Naomi Watts - Mulholland Drive
Philip Seymour Hoffman - Before the Devil Knows You're Dead
Robert Shaw - Jaws
Sigourney Weaver - Aliens
Heath Ledger - The Dark Knight
Benecio Del Toro - 21 Grams
Bjork - Dancer in the Dark
Daniel Day-Lewis - There Will Be Blood
Forest Whitaker - The Last King of Scotland
Laura Linney - You Can Count On Me
Jack Nicholson - One Flew Over The Cuckoo's Nest
Samuel L. Jackson - Pulp Fiction
Marlon Brando - The Godfather
Al Pacino - Dog Day Afternoon
Dustin Hoffman - Kramer vs. Kramer
Ethan Hawke - Before The Devil Knows YOu're Dead
Patty Duke - The Miracle Worker
Anne Bancroft - The Miracle Worker
Denzel Washington - Training Day
Robert DeNiro - Raging Bull
Jon Voight - Runaway Train
Paul Newman - The Hustler
John Hurt - The Elephant Man
Alec Baldwin - Glengarry Glen Ross
James Earl Jones - Field of Dreams
Meryl Streep - Kramer vs. Kramer
Paul Newman - The Verdict
Humphrey Bogart - Casablanca
Whoopi Goldberg - The Color Purple
Meryl Streep - Sophie's Choice
Marlon Brando - On the Waterfront
Bill Murray - Groundhog Day
Your faves?
3:09 PM PT: Have to go offline for a while - fantastic contributiuons!! Keep it up - we could use this whole thread for a reference! Back as soon as I can.