One of my favorites is Pulp fiction. Not that im a brainless fan of Quentin Tarentino, it just had great dialoque.
Scary Movie 3, American Pie, Requiem For A Dream, Trainspotting, Groundhog Day, Children Of Men, Hostel, Back To The Future, SAW 3...ugh, loads. I can't really choose one.
Requiem for a Dream, Fight Club, The Butterfly Effect, Cherry Crush, American History X, Cruel Intentions, etc.
Definately Garden State, the Notebook, The Secret Window, Texas Chainsaw Massacre, The Nitemare Before Christmas, Edward Scissorhands... But I'm more of a book person myself. :]
The Caveman's Valentine Once Were Warriors Swingers Paint Your Wagon Amores Perros The Guardian Rocky Balboa Naked The Bishop's Wife
Mine would have to be Friday. Gotta love Clerks I and II, and of course Jay and Silent Bob, Dogma and all the other Kevin Smith movies ;] Oh, and you can't forget about Harold and Kumar Go to White Castle/ Guantanama Bay. Those would have to be my favorite movies :[ EDIT: Shit, forgot, I love every single American Pie movie D:
Fight Club, Requiem for a Dream, A Clockwork Orange and The Science of Sleep. Just off the top of my head.