Daniel Day-Lewis and Tilda Swinton swept Britain to Oscar glory in Los Angeles while No Country For Old Men was the biggest film of the ceremony.
Day-Lewis, 50, as predicted, won his second best actor Academy Award for his towering performance as a ruthless, malevolent oilman in There Will Be Blood.
Swinton, 47, landed the best supporting actress gong for her role as a ruthless corporate lawyer in the George Clooney movie Michael Clayton.
The 80th Academy Awards named French actress Marion Cotillard as best actress for her role as singer Edith Piaf in the biopic La Vie en Rose.
The 32-year-old beat Julie Christie to the title just weeks after her surprise victory over the British veteran at the Baftas.
The film that dominated the night at Hollywood's Kodak Theatre was No Country For Old Men, the Coen brothers' violent neo-western.
It won four of its eight nominations, beating British film Atonement to best picture, and scooping best director. It also took the prize for best supporting actor for Spanish actor Javier Bardem, and adapted screenplay.
London-born Swinton provided one of the most amusing speeches of the ceremony when she thanked her agent, but not in the usual fashion, saying as she held up her statuette: "I have an American agent who is the spitting image of this.
"Really, truly, the same shaped head and it has to be said the buttocks. I'm going to give this to him because there's no way I'd be in America, even on a plane, if it wasn't for him."
She also dedicated her award to Clooney, the film's producer and star, joking: "Seeing you climb into that rubber batsuit from Batman and Robin, the one with the nipples, every morning under your costume, on the set, off the set, hanging upside-down at lunch, you rock, man. Thank you, thank you, thank you."
Day-Lewis, who holds joint Irish and British citizenship, and received his first Oscar for My Left Foot in 1990, picked up his second Academy Award from Helen Mirren, recipient of last year's best actress gong.
"That's the closest I'll ever come to getting a knighthood, so thank you," he joked.
Perhaps drawing inspiration from his violent character Daniel Plainview in There Will Be Blood, he thanked "the members of the academy for whacking me with the handsomest bludgeon in town.
"I'm looking at this gorgeous thing you've given me and I'm thinking back to the first devilish whisper of an idea that came to him and everything since and it seems to me that this sprang like a golden sapling out of the mad, beautiful head of (director and writer) Paul Thomas Anderson," he said.
* These are the winners of the 80th Academy Awards:
Best picture: No Country For Old Men
Best director: Joel and Ethan Coen, No Country For Old Men
Best actor: Daniel Day-Lewis, There Will Be Blood
Best actress: Marion Cotillard, La Vie En Rose
Best supporting actress: Tilda Swinton, Michael Clayton
Best supporting actor: Javier Bardem, No Country For Old Men
Best foreign language film: The Counterfeiters (Austria)
Best animated feature film: Ratatouille
Best adapted screenplay: No Country For Old Men
Best original screenplay: Juno
Best music (score): Atonement
Best music (song): Falling Slowly, Once
Best documentary feature: Taxi To The Dark Side
Best documentary short subject: Freeheld
Best visual effects: The Golden Compass
Best Cinematography: There Will Be Blood
Best art direction: Sweeney Todd: The Demon Barber Of Fleet Street
Best animated short film: Peter And The Wolf
Best short film: Le Mozart Des Pickpockets
Best costume design: Elizabeth: The Golden Age
Best make-up: La Vie En Rose
Best sound mixing: The Bourne Ultimatum
Best sound editing: The Bourne Ultimatum
Best film editing: The Bourne Ultimatum