Anything by Stanley Kubrick: A Clockwork Orange, Dr. Strangelove, Barry Lyndon, Lolita, Killer's Kiss, The Shining, Spartacus, Paths of Glory, Full Metal Jacket, etc.
Anything by Alfred Hitchcock: Vertigo, North by Northwest, Rear Window, The Trouble With Harry, Psycho, Strangers on a Train, Rope, etc.
Anything by Akira Kurosawa: Yojimbo, Seven Samurai, Throne of Blood, Kagemusha, The Hidden Fortress, Rashomon, High and Low, Dersu Uzala, Sanjuro
Anything by David Lynch: Mulholland Drive, Blue Velvet, Eraserhead, The Elephant Man, Lost Highway, etc.

that's just a start

I recently rewatched Heathers and was bitterly disappointed. That film did not age well at all. What was once biting, dark humor is largely passe nowadays. There are still some pretty great moments but the film just seems to take itself a little too seriously.

Oh, and I just bought Children of Men on DVD. That movie should be required viewing for everyone. It's even better the third time than it was the first (which had me spending much of the movie slack-jawed and in awe of what was happening onscreen).

I also bought Dr. Strangelove, which is still probably the funniest movie ever created (with Blazing Saddles nipping at its heels).

I just can't agree with you - I think Heathers has aged very well, has a great performance by Christian Slater, and has the high-school setting mentioned by the OP.

Also - to disagree with you again - - Children of Men - what a dull and uninspiring film!

Slightly more on topic: I third or fourth Donnie Darko, and second Pan's Labyrinth

More High School movies - Battle Royale & Back to the Futrue

Also, not a movie I know but how about Twin Peaks