The African Queen (1951) - A classic, must-see, Bogart/Hepburn movie.
How to Succeed in Business (Without Really Trying) (1967) - This is one of my all-time favorite comedies and favorite musicals. I fell in love with this back in high school (and wouldn't recommend it for anyone any younger).
The Secret of Kells (2009) - This is an amazingly well done (different) animated feature. The story was intriguing, though a little scary for really young kids.
The Iron Giant (1999) - This is another great animated feature that can be enjoyed by all ages.
Peter and the Wolf (2006) - This is a short one, but a great, stop-motion adaptation of the story (and probably makes your kids smarter for listening to Prokofiev's beautiful score).