In no particular order:
Paths of Glory: My favorite Kubrick film for two reasons: 1-Kirk Douglas and 2-the intense climax. Much more sentimental than Full Metal Jacket, but Kubrick also makes a point of examining that sentiment in the final scene.
Into the Wild: Beautifully photographed and acted. This character study is an excellent adaptation of the original non-fiction book about a college grad who burns all of his money, ditches his car, and lives the life of a tramp, wandering across the American northwest and Alaska.
M: Peter Lorre steals the show. A fan-freaking-tastic performance that actually garners sympathy for a child murderer.
Crimes and Misdemeanors: Woody Allen gets massive kudos from me for comparing, contrasting, and inverting comedy and tragedy in this film. Screenwriting at its finest.
Rear Window: John Michael Hayes manages to gloss over Hitchcock's misanthropy (just a bit) with some warm, engaging characters. Also, Alfred Hitchcock, Jimmy Stewart, and Princess Grace.
Vertigo: Like someone took Rear Window and kicked the crap out of its soul. Dark and haunting, visually striking, Vertigo is Hitchcock at the top of his game.
Short Cuts: I almost put MASH on here, but Short Cuts deserves to be on this list much more. The best Altman film that I've seen, and an interesting adaptation of many of Raymond Carver's short stories.
Days of Heaven: Oh my God, there's not a single frame of this movie that isn't beautiful.
Straw Dogs: In Sam Peckinpah's world, sexual tension and inferiority lead to rape and violence. This movie is so brutal that it's hard to watch, and that's what I like about it.
Last Tango in Paris: For all its fucked-upedness, Brando blew his acting wad making this picture (in more ways than one). His monologue at the casket of his dead wife makes me cry almost every time I see it.
I'd also give out honorable mentions to Spirited Away, Barton Fink, Pulp Fiction, Ghostbusters, and The Shawshank Redemption.