Fight club is too mainsteam to be cult, ya?

1941 It's bad but it still makes me laugh

I would say a cult film doesn't require most to dislike it, just most to come out of the theater saying 'what the hell was that movie about?'. And a few, the cultists, having something that appealed to them about the movie, even if they couldn't understand why.

From these that others have picked, I'll go along with.

Blade Runner
Rocky Horror Picture Show is probably the cult of cult films.
Clockwork Orange
Young Frankenstein
Labyrinth
Tron
Spaghetti westerns of Clint Eastwood.
The Hitchhikers Guide to the Galaxy 42. If you know that, you know all you need to know.
Thumbs up to Sri Lumpa. The Princess Bride. Great movie. Alan Parson Project music for the soundtrack. Inconceivable.

And then I have to agree with Hawk:

Monty Python and the Holy Grail

"Out of curiosity, has anyone here seen Night of the Lepus?
It's the greatest giant killer bunny rabbit movie ever. Now that's a true cult film."

That big bunny got nothing on one with little sharp nasty teeth!!

Does the Planet of the Ape pentalogy count?

 no as its cult becasue few people heard of it

They Live

suprised to see no mention of Memento.

 You're being sarcastic.... right?

Kung Pow: Enter The Fist

Super Troopers (dunno how cult this is) 

HAHA, i gotta say, Super Troopers is somewhat cult, as not many people remember it, but the people who do tend to love it like crazy. Broken Lizard films could be considered somewhat cult films.

Oh, for the people saying certain films arent cult because they are too mainstream, you have to remember a lot of these movies started out cult, no one knowing it, then worked their way up more into the mainstream.

I would have to say Serenity is an awesome example of a Cult film, considering it had a MASSIVE fanbase before the movie came out. Hell, if you know the story, that movie came out just because of the crazy work that fanbase put into it. Like fans literally were donating time and money to get that film made, and had they not, it would never have see the light of day.

By the way, if anyone likes that movie, plans on a 2nd one are being made.