1939
Union Pacific (Cecil B. DeMille)*
1946
Brief Encounter (above, David Lean), Maria Candelaria / Portrait of Maria (Emilio Fernández), Velikiy perelom / The Turning Point (Fridrikh Markovitch Ermler), La symphonie pastorale (Jean Delannoy), Die Letzte Chance / The Last Chance (Leopold Lindtberg), Muzi bez krídel / Men Without Wings (Frantisek Cáp), Roma, città aperta / Rome, Open City (Roberto Rossellini), Neecha Nagar / Lowly City (Chetan Anand), Hets / Torment (Alf Sjöberg), The Lost Weekend (Billy Wilder), De Røde enge / The Red Earth (Bodil Ipsen and Lau Lauritzen)
1947
Romantic and Psychological Films: Antoine et Antoinette / Antoine and Antoinette (above, Jacques Becker), Adventure and Detective Films: Les Maudits / The Damned (René Clément), Socially Minded Films: Crossfire (Edward Dmytryk), Musical Comedies: Ziegfeld Follies (Vincente Minnelli), Animated Films: Dumbo (Ben Sharpsteen for Walt Disney), Documentaries: Floods in Poland (short film by Jerzy Bossak and Waclaw Kazmierczak)**
1949
The Third Man (Carol Reed)
1951
Miracolo a Milano / Miracle in Milan (top, Vittorio De Sica), Fröken Julie / Miss Julie (bottom, Alf Sjöberg)
1952
Due soldi di speranza / Two Cents Worth of Hope (top, Renato Castellani), The Tragedy of Othello: The Moor of Venice / Othello (bottom, Orson Welles)
1953
Le Salaire de la peur / The Wages of Fear (Henri-Georges Clouzot)
1954
Jigokumon / Gate of Hell (Teinosuke Kinugasa)
1955
Marty (Delbert Mann)
1956
Le Monde du silence / The Silent World (Jacques-Yves Cousteau and Louis Malle)
1957
Friendly Persuasion (William Wyler)
1958
Letyat zhuravli / The Cranes are Flying (Mikhail Kalatozov)
1959
Orfeu Negro / Black Orpheus (Marcel Camus)
1960
La Dolce vita (Federico Fellini)
1961
Une aussi longue absence / The Long Absence (Henri Colpi), Viridiana (Luis Buñel)
1962
O Pagador de Promessas / Keeper of Promises (Anselmo Duarte)
1963
Il Gattopardo / The Leopard (Luchino Visconti)
1964
Les Parapluies de Cherbourg / The Umbrellas of Cherbourg (Jacques Demy)
1965
The Knack …and How to Get It (Richard Lester)
1966
Signore & signori / The Birds, the Bees and the Italians (Pietro Germi), Un homme et une femme / A Man and a Woman (Claude Lelouch)
1967
Blowup (Michelangelo Antonioni)
1969
If? (Lindsay Anderson)
1970
M*A*S*H (Robert Altman)
1971
The Go-Between (Joseph Losey)
1972
La Classe operaia va in paradiso / The Working Class Goes to Heaven (above, Elio Petri), Il Caso Mattei / The Mattei Affair (Francesco Rosi)
1973
The Hireling (Alan Bridges), Scarecrow (Jerry Schatzberg)
1974
The Conversation (Francis Ford Coppola)
1975
Chronique des années de braise / Chronicle of the Years of Fire (Mohammed Lakhdar-Hamina)
1976
Taxi Driver (Martin Scorsese)
1977
Padre Padrone / My Father My Master (Paolo Taviani and Vittorio Taviani)
1978
L'Albero degli Zoccoli / The Tree of Wooden Clogs (Ermanno Olmi)
1979
Apocalypse Now (Francis Ford Coppola), Die Blechtrommel / The Tin Drum (Volker Schlöndorff)
1980
All That Jazz (Bob Fosse), Kagemusha (above, Akira Kurosawa)
1981
Czlowiek z zelaza / Man of Iron (Andrzej Wajda)
1982
Missing (Costa-Gavras), Yol (Yilmaz Güney)
1983
Narayama Bushiko / The Ballad of Narayama (Shohei Imamura)
1984
Paris, Texas (Wim Wenders)
1985
Otac na sluzbenom putu / When Father Was Away on Business (Emir Kusturica)
1986
The Mission (Roland Joffé)
Sous le soleil de Satan / Under the Sun of Satan (Maurice Pialat)
1988
Pelle erobreren / Pelle the Conqueror (Bille August)
1989
Sex, Lies and Videotape (Steven Soderbergh)
1990
Wild at Heart (David Lynch)
1991
Barton Fink (Joel Coen and Ethan Coen)
1992
Den Goda viljan / The Best Intentions (Bille August)
1993
Ba wang bie ji / Farewell My Concubine (Chen Kaige), The Piano (Jane Campion)
1994
Pulp Fiction (Quentin Tarantino)
1995
Underground (Emir Kusturica)
1996
Secrets & Lies (Mike Leigh)
1997
Ta'm e guilass / Taste of Cherry (Abbas Kiarostami), Unagi / The Eel (Shohei Imamura)
1998
Mia aioniotita kai mia mera / Eternity and a Day (Theo Angelopoulos)
1999
Rosetta (Luc Dardenne and Jean-Pierre Dardenne)
2000
Dancer in the Dark (Lars von Trier)
2001
La Stanza del figlio / The Son's Room (Nanni Moretti)
2002
The Pianist (Roman Polanski)
2003
Elephant (Gus Van Sant)
2004
Fahrenheit 9/11 (Michael Moore)
2005
L'Enfant / The Child (Luc Dardenne and Jean-Pierre Dardenne)
2006
The Wind that Shakes the Barley (Ken Loach)
2007
4 luni, 3 saptamini si 2 zile / 4 Months, 3 Weeks, and 2 Days (Cristian Mungiu)
* The 1939 prize was given retroactively at the 55th ceremony in 2002. The 1939 festival was cancelled because of World War II.
** The 1947 winners were selected according to particular genres. The awards given out that year were not referred to as "Grand Prix."
Due to a lack of funds, there was no festival in 1948 and 1950. The 1968 festival came to a halt because of the student protests that paralyzed France. Thus far, no retroactive awards have been handed out for that particular year, though there's always hope.
Prior to 1955, the Cannes Festival's top prize was called the "Grand Prix du Festival International du Film."
Source: IMDb, and Cari Beauchamp and Henri Béhar's Hollywood on the Riviera.