The Petrified Forest (1936). A surprisingly intelligent and witty gangster siege movie starring Leslie Howard, Bette Davis and Humphrey Bogart.
Sib (The Apple) (1998). This Iranian film by Samira Makhmalbaf is about two young girls who have spent all their lives locked up by their parents. When I read the summary of the story I expected a serious, social-realist film about injustice and cruelty, but it's nothing like that. Makhmalbaf asked the parents and the children to play themselves in this movie, and she explores their lives without making the expected easy judgements. What you get as a result is an extremely moving film (I must admit I cried several times, as much at the old man's sense of humiliation as at the children's suffering - I also laughed a great deal, especially when Makhmalbaf follows the young girls outside the house). I can't recommend this film enough.
Incidentally, if you haven't seen any modern Iranian films, I suggest you go and find some on DVD. In the last twenty years Iranian cinema has produced some really high quality films.
The true mystery of the world is the visible, not the invisible