1. Robert De Niro (Taxi Driver)
2. Klaus Kinski (Aguire: Wrath of God)
3. Jack Nicholson (One Flew Over the Cuckoo's Nest)
4. Paul Newman (The Hustler)
5. Daniel Day Lewis (There Will Be Blood)
6. Edward Norton (American History X)
7. Heath Ledger (The Dark Knight)
8. Al Pacino (The Godfather part II)
9. Christoph Waltz (Inglorious Basterds)
10. Isabelle Adjani (Possession 1981)

11. Gary Oldman (Leon The Professional)
12. Jon Voight (Midnight Cowboy)
13. Harvey Keitel (Bad Lieutenant)
14. Michael Fassbender (Shame)
15. Eric Bana (Chopper)
16. Marlon Brando (Apacolypse Now)
17. Emily Watson (Breaking the Waves)
18. Michael Rooker (Henry: Portrait of a Serial Killer)
19. Ellen Burstyn (Requiem of a Dream)
20. James Stewart (Vertigo)
    Honorable Mention:
    Christian Bale (American Psycho)
    Those are just off the top of my head. I know I'm missing a lot of good ones. Its hard to choose just 10 (or just 100 for that matter).

A great performance is a great performance no matter whether it's considered lead or supporting and the term
actor
applies to females as well, I assume. So my list should include Liv Ullman in Face to Face as well as Kim Stanley in The Goddess.

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Daniel Day Lewis In the Name of the Father and My Left Foot
Robert Mitchum Cape Fear and The Night of the Hunter
George C. Scott The Hospital
Al Pacino Donnie Brasco and Dog Day Afternoon
Marlon Brando A Streetcar Named Desire and Reflections in a Golden Eye
Dustin Hoffman Straight Time
Paul Newman Hud
Michael Keaton Birdman
Albert Finney Alpha-Beta

1. Jimmy Stewart(Harvey)
2. Paul Newman (Hud)
3. Montgomery Clift (A Place In The Sun)
4. Marlon Brnado (Streetcar Named Desire)
5. Henry Fonda(The Grapes Of Wrath)
6. George C Scott (The Hustler ect)
7. Lee J. Cobb (12 Angry Men)
8. Al Pacino (Godfather)
9. Christian Bale(The Machinist)
10. Brad Pitt (The Assassination By Jessie James By The Coward Robert Ford )

in no particular order (screw that, it's too hard guys)
Clint Eastwood - Unforgiven
Al Pacino - The Godfather Part II
Paul Newman - The Verdict
Marlon Brando - A Streetcar named Desire
Robert de niro - Taxi Driver
Henry Fonda - On Golden pond
Russell Crowe - The Insider
Peter Finch - Network
Sean Penn - Mystic River
Heath Ledger - The Dark Knight
Edward Norton - American History X
Hate is baggage. Life is too short to be pissed off all the time

Paul Newman (The Hustler)
Denzel Washington (Training Day)
Tom Hanks (Cast Away)
Nicolas Cage (Bringing Out the Dead)
Haley Joel Osment (The Sixth Sense)
Jack Nicholson (The Shining)
Jack Nicholson (The Crossing Guard)
Meg Ryan (When a Man Loves a Woman)
Al Pacino (Insomnia)
Robin Williams (One Hour Photo)
I couldn't say which performance is better. I love them all equally.
X

So many good choices. Here's some that may have been overlooked:
Richard Pryor Richard Pryor Live
Gloria Swanson Sunset Boulevard
Mia Farrow Rosemary's Baby
Liv Ullman Face to Face & Scenes from a Marriage
Deborah Kerr The Innocents
Anne Bancroft The Graduate & The Miracle Worker
Morgan Freeman Street Smart
Glenda Jackson Marat/Sade
Kim Stanley The Goddess
Peter O'Toole Beckett

Just a note: I realize my list, which I just though up on the spot, is fairly modern. I've seen a handful of classics, but I should watch more films from back in the day, for instance I recently watched Who's Afraid of Virginia Woolf, and his performance could definitely go on a top ten list for mebut for this list's modernity I'll subtitle it "top ten actor performances of recent years."
Rod Steiger - In the Heat of the Night
Johnny Depp - Ed Wood
Brad Pitt - Moneyball
Jack Nicholson - One Flew Over the Cuckoo's Nest
Al Pacino - Dog Day Afternoon
Leonardo Dicaprio - The Departed
Jesse Eisenberg - The Social Network
Jeff Bridges - The Big Lebowski*
Clint Eastwood - Unforgiven
Javier Bardem - No Country For Old Men
I think many performances from Coen Bros films could contend for top tensThey're ingenious filmmakers for sure, but one of things I think they do every picture is know how to bring out first-rate, incomparable acting in their stars.

1). Jose Ferrer - Cyrano De Bergerac
2). Humphrey Bogart - Casablanca
3). James Cagney - Yankee Doodle Dandy and One, Two, Three
4). Kevin Costner - JFK
5). Peter O'Toole - Lawrence of Arabia
6). George C. Scott - Patton
7). Val Kilmer - Tombstone
8). Jose Ferrer - Moulin Rouge
9). Denzel Washington - Malcolm X, Crimson Tide and A Soldier's Story
10). Burt Lancaster - The Train
Honorable Mention:
Jimmy Stewart - Flight of the Phoenix
Paul Scofield - A Man for All Seasons
Paul Newman - The Hustler
Steve McQueen - Bullitt
Robert Mitchum - Farewell My Lovely
Errol Flynn - All of his Swashbucklers (The Adventures of Robin Hood, Captain Blood, the Sea Hawk) and Gentleman Jim

De Niro - Taxi Driver
Sellers - Dr Strangelove
Scott - Dr Strangelove
Hoffman - Rain Man
Nicholson - Chinatown
Stewart - Mr Smith Goes to Washington
Day-Lewis - There Will Be Blood
Lemmon - Some Like It Hot
Grant - Notorious
Fonda - 12 Angry Men
"My car is outside."
"Naturally."

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No particular order and probably not my complete list
Daniel Day Lewis - There Will Be Blood / Gangs of New York / The Crucible
Robert Deniro - Raging Bull / Taxi Driver / Goodfellas / Godfather 2 / Heat
Anthony Hopkins - Silence of the Lambs
Dustin Hoffman - The Graduate
Kevin Spacey - Usual Suspects / American Beauty / LA Confidential
Sam Jackson - Pulp Fiction
Ben Kingsley - Gandhi
Malcolm McDowell - A Clockwork Orange
Val Kilmer - Tombstone / Heat
Nicholas Cage - Leaving Las Vegas / Adaptation
Joe Pesci - Goodfellas / Raging Bull
Heath Ledger - Dark Knight
Morgan Freeman - Shawshank Redemption / Unforgiven
Sasha Baron Cohen - Borat
Russel Crowe - A Beautiful Mind / Gladiator
Tom Hanks - Forrest Gump
Jake Gyllenhaal - Donnie Darko
Jack Nicholson - The Shining
Christian Bale - American Psycho / The Machinist
Ed Norton - Fight Club / American History X
Mel Gibson - Braveheart
Paul Newman - The Hustler
Sylvester Stallone - Rocky 1
Emile Hirsch - Into the Wild
R. Lee Emery - Full Metal Jacket
Viggio Mortenson - Eastern Promises
Marlon Brando - On the Waterfront
Mark Wahlberg - Boogie Nights
Clint Eastwood - Unforgiven / Good Bad and the Ugly
Gene Hackman - Unforgiven / The French Connection
Peter O'Toole - Lawrence of Arabia
Johnny Depp - Blow / Donnie Brasco
Brad Pitt - Inglorius Basterds / Snatch / Fight Club
Steve Buscemi - Resevoir Dogs / Fargo
Casey Afleck - The Assasination of Jessie James
Denzel Washington - American Gangster
Javier Bardem - No Country for Old Men
Gary Oldman - The Professional
James Dean - Rebel Without a Cause
Joaquin Phoenix - Walk the Line
Tommy Lee Jones - The Fugitive
Colin Firth - The Kings Speech
Tom Cruise - Magnolia
Don Cheadle - Hotel Rwanda
Terrence Howard - Hustle & Flow
Matt Damon - Talented Mr. Ripley
Al Pacino - Godfather 1 & 2 / Scarface / Heat
Leo DiCaprio - The Aviator / The Departed
Phillip Seymour Hoffmann - Capote
Jimmy Stewart - Rear Window / It's a Wonderful Life
William H. Macey - Fargo

In no particular order.

1. Steve Mc Queen, The Sand pebbles
2. Brando, in Godfather
3. Eastwood, The Good the bad and the ugly
4. Anthony Hopkins, The Silence of the Lambs
5. Jack Nicholson, One flew over the Cuckoo's Nest
6. Robert De Niro, Raging Bull
7. Adolph Caesar, A Solider's Story
8. Gregory Peck, To Kill a Mockingbird
9. Dustin Hoffman, The Graduate
10. Richard Burton, Who's afraid of Virginia Woolf

You have some great ones there. I would add:

1. James Cagney (Love Me or Leave Me)
2. Humphrey Bogart (The Caine Mutiny)
3. Robert Mitchum (Cape Fear)
4. Henry Fonda (12 Angry Men)
5. Larry Parks (The Jolson Story)
6. James Cagney (Yankee Doodle Dandy)
7. James Cagney (White Heat)
8. Burt Lancaster (Atlantic City)
9. Gary Cooper (Sergeant York)
10. Clark Gable (GETW)

In no particular order;
Marlon Brando. On the waterfront
Jack Nicholson. One flew over the cuckoo's nest
Robert Deniro. Raging bull
Humphrey Bogart. Casablanca
James Dean. East of eden
Laurence Olivier.Term of trial
Michael Caine. Alfie
Paul Newman. The hustler
Al Pacino. The Godfather
Alan Ladd. Shane
Alan Arkin. The heart is a lonely hunter

'Is it just me or does it seem like everyone here mentions movies that are really old only because it sounds cooler than say a Leonardo DiCaprio in the The Aviator or a Denzel Washington in Training Day?
No offence and all but it just seems like most people here are just full of sh*t'
WTF is with you? First off Denzel in Training Day was over the top. And Leo in Aviator was sub-par (Accent mostly)
and These are people's opinions. You really to get offensive cause you don't agree, But let me tell you this, kiddo. Most of the best acting performances are from the past. Such as Peter o' Toole, Paul Newman, Richard Burton, Laurence Oliver, Marlon Brando, all have given some of the best performances in history.
Just because it's not in your generation does not mean they're bad. And De Niro in Taxi Driver and Bogart in Casablanca are average.

I agree DiCaprio was sensational in The Aviator.
Daniel Day-Lewis - There Will Be Blood
Al Pacino - Godfather Part II
Renee Falconetti - The Passion of Joan of Arc
Daniel Day-Lewis - My Left Foot
Samuel L Jackson - Pulp Fiction
Christopher Lloyd - Back to the Future (Sorry but I love it)
Heath Ledger - The Dark Knight
Charlie Chaplin - City Lights
Dustin Hoffman - The Graduate
Harrison Ford - Star Wars

Is it just me or does it seem like everyone here mentions movies that are really old only because it sounds cooler than say a Leonardo DiCaprio in the The Aviator or a Denzel Washington in Training Day? No offence and all but it just seems like most people here are just full of sh*t.
LOL
I know, I thought so too! I don't give two freaking cents about Humpfrey Bogart in Casablanca or Robert Deniro in Taxi Driver. I thought they were average performances, even weak if I really want to be honest. I hate when people go with the crowd. Isn't it better to make your top ten more of your own?
Sorry if I seem like that to you though! XD
In my opinion, in no order at the moment:
Dustin Hoffman (Midnight Cowboy)
Al Pacino (Scarface or Dog Day Afternoon)
Gary Oldman (Sid and Nancy, Immortal Beloved, or Dracula)
James Stewart (Mr. Smith Goes to Washington)
Robert Deniro (Raging Bull)
James Dean (Giant)
Jon Voight (Midnight Cowboy)
Daniel Day Lewis (There Will Be Blood)
George C Scott (Patton)
Scott Wilson (The Ninth Configuration)
Alfred Molina (Prick Up Your Ears)
Tom Hanks (Forrest Gump)
Lawereance Olivea or however you spell his name (Marathon Man)
Paul Muni (Scarface: Shame of the Nation)
I still have to see a lot more movies
Currently obsessed with:
Tailor Made (I Love Money) Oh-la-la!!!

Is it just me or does it seem like everyone here mentions movies that are really old only because it sounds cooler than say a Leonardo DiCaprio in the The Aviator or a Denzel Washington in Training Day?
No offence and all but it just seems like most people here are just full of sh*t.
But hey, thats just my opinion!
Just so you know, I have seen a few (if not most) of the above mentioned movies and although I think these guys were brilliant, I dont think most of them make for the "Top ten greatest actor performances" of all time.

In no order:
Peter O'Toole - Lawrence of Arabia
Gregory Peck - To Kill a Mockingbird
Marlon Brando - On The Waterfront
Jimmy Stewart - It's a Wonderful Life
Henry Fonda - 12 Angry Men
Spencer Tracy - Captain's Courageous
Jack Nicholson - Chinatown
Orson Welles - Citizen Kane
There are many more, but I'm tired so I'm stopping:D

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