I didn't think Dr Strangelove was a cult film. It is one of my favorites, and probably my favorite Kubrick film, even though my friends try to argue that A Clockwork Orange is better.
I might have to go with Big Lebowski, or maybe Office Space. One of those two.
This is Spinal Tap. Might as well thrown in Meathead's The Princess Bride also. Aw heck, let's get another Christopher Guest movie in there, Best of Show. That might be the best of the bunch.