I like most genres of movies. Action, Adventure, Comedy, Romantic Comedy, Science Fiction, Fantasy, B movies, Martial Arts, Jackie Chan (he's in a class of his own), and probably a few others which I'm forgetting. My collection is consequently pretty varied. I'm currently working on cataloging my movie collection, which I'll put up on this website once I'm done.
I'm also fond of learning about the history of American movies. Netflix is very useful in this regard. It enables me to see movies like Fast Times at Ridgemont High, American Graffiti, and The Graduate — movies which have had a significant impact on the direction of film making.
I'm also very fond of watching DVD special features. Most of the time they're not very interesting, of course, but the ones which are can be fascinating. The special edition of The Adventures of Robin Hood (with Errol Flynn) had a feature on the history of Technicolor which was engrossing.