Oh Performances...

Listy list list...
Top 10 Best Performances by an Actor(no order):
Kirk Douglas in Ace in the Hole
Kirk Douglas in The Bad and the Beautiful
Humphrey Bogart in In a Lonely Place
Rod Steiger in The Pawnbroker
John Wayne in The Searchers
Ben Gazzara in The Killing of a Chinese Bookie
Elliot Gould in MASH
Harry Dean Stanton in Paris, Texas
Robert Ryan in On Dangerous Ground
Jack Nicholson in The Passenger
Honorable mentions: Henry Fonda in My Darling Clementine or The Grapes of Wrath, Lee Marvin in Point Blank or The Big Heat, Jeff Bridges in The Big Lebowski, Sterling Hayden in The Killing, Alain Delon in something, and Arnold Schwarzenegger in practically all his "fun for the family" films(he might be the greatest comedic actor of all-time)

Top 10 Best Performance by an Actress(no order):
Oksana Akinshina in Lilya 4-Ever
Gena Rowlands in A Woman Under the Influence
Gloria Grahame in In a Lonely Place
Laura Dern in Inland Empire
Naomi Watts in Mulholland Dr.
Bjork in Dancer in the Dark
Barbara Loden in Wanda
Nicole Kidman in Dogville
Ida Lupino in On Dangerous Ground
Samantha Morton in Morvern Callar
Honorable mentions: Gloria Grahame in The Big Heat, Sarah Polley in The Sweet Hereafter, Faye Wong in Chungking Express, Chantal Goya in Masculin, feminin, Kyoka Kishida in Woman in the Dunes, Bibi Andersson in The Seventh Seal, and Makiko Esumi in Pistol Opera

Not sure about these...