The critically-acclaimed Crash was the winner at France's Deauville Film Festival, which celebrates US movies.
Matt Dillion joined director Paul Haggis to promote Crash
The film, directed by Paul Haggis, has a star-studded cast including Sandra Bullock, Don Cheadle and Matt Dillon.
The Jury Prize, considered the runner-up award, was shared between Keane and On the Outs, about three young women living in New Jersey.
Transamerica, about a male-to-female transsexual's relationship with her son, won the best screenplay prize.
The film stars Desperate Housewives actress Felicity Huffman as a transsexual who discovers she fathered a child, who she meets when he is a teenager.
Huffman won the best actress award at the Tribeca Festival in New York earlier in the year for her performance in the drama.
Keane centres on a schizophrenic man, played by Damian Lewis, and his search for his daughter thought to have been kidnapped at a bus station.
On the Outs traces the lives of three young women - one a drug dealer, one an addict and the other a pregnant teenager - and the limited choices they have for their future.
At the prize-giving ceremony, the co-directors of On the Outs criticised US authorities.
Michael Skolnik told the audience Hurricane Katrina reinforced the message of their film by showing "it's no longer a secret we have poor people in our country".