Blade Runner—Beautiful, symbolically rich film that leaves the viewer with hours worth of things to contemplate.
2001: A Space Odyssey—See above.
Il mio nome è Nessuno (My Name is Nobody)—Fairly obscure Spaghetti Western Comedy that most people write off as silly slapstick... There’s plenty of slaptick to be sure, but there’s also some good thought provoking satire here too. The movie has a lot to say about the descent of the Western into an exploitation genre, and some worthy thoughts on the nature and need for heroes... The cinematography is flooringly beautiful too.
Hmm.... I guess I like thought provoking, visually striking films.
I've posted this before, but it's such a great trailer for a great movie...
[youtube]http://www.youtube.com/watch?v=2RYq1PLdT0s[/youtube]

This.