Self-explanatory, or it should be. Follow my queue and have fun widdit.
1920s:
"The Gold Rush," Charlie Chaplin (1925)
Honorable Mention: "The Kid," Charlie Chaplin (1921)
(I'm pretty sure those are the only two 1920s films I've seen thus far

)
1930s:
"All Quiet on the Western Front," Lewis Milestone (1930)
HM: "The Wizard of Oz," Victor Fleming (1939), "Mr. Smith Goes to Washington," Frank Capra (1939)
1940s:
"Casablanca," Michael Curtiz (1942)
HM: "The Great Dictator," Charlie Chaplin (1940), "Beauty and the Beast," Jean Cocteau (1946)
1950s:
"Ikiru," Akira Kurosawa (1952)
HM: "The Searchers," John Ford (1956), "Wild Strawberries," Ingmar Bergman (1957)
1960s:
"The Good, the Bad and the Ugly," Sergio Leone (1966)
HM: "2001: A Space Odyssey," Stanley Kubrick (1968), "The Magnificent Seven," John Sturges (1960)
1970s:
"All the President's Men," Alan J. Pakula (1976)
HM: "The Wicker Man," Robin Hardy (1973), "Network," Sidney Lumet (1976)
1980s:
"The Shining," Stanley Kubrick (1980)
HM: "Amadeus," Milos Forman (1984), "Do the Right Thing," Spike Lee (1989)
1990s:
"The Big Lebowski," Joel and Ethan Coen (1998)
"Fargo," Joel and Ethan Coen (1996), "Unforgiven," Clint Eastwood (1992)
2000s:
"Mulholland Dr.," David Lynch (2001)
"There Will Be Blood," Paul Thomas Anderson (2007), "Inglourious Basterds," Quentin Tarantino (2009)
It was soooooo hard to do the honorable mentions for the 1950s; that was easily the best decade for foreign art house and American Westerns, two of my favorite genres. Otherwise fairly smooth if probably imperfect. Thoughts? Your picks?