The Apartment is a wonderful movie.
I love some Hitchcock- Vertigo and North by Northwest being my favorites.
I am a huge Citizen Kane fan, I have no problems whatsoever when people call it the greatest film of all time.
Casablanca, Gone With the Wind, Clockwork Orange, The Searchers and It's a Wonderful Life are also up there for me. I love old movies. Oh, and make fun of me if you want, but Meet Me In St Louis and Singing in the Rain too.