Studio Ghibli has a lot of fantastic films for children that can still be enjoyed by their parents. 'My Neighbor Totoro', 'Ponyo', 'Kiki's Delivery Service', 'Castle in the Sky', 'Spirited Away', and 'The Cat Returns' all come to mind. Though don't assume they're all for kids because they're animated - 'Princess Mononoke' is very violent.
Then there's just showing them older films in general. I watched a ton of Fred Astaire, Gene Kelly, Audrey Hepburn, and Marilyn Monroe movies when I was little - good music, dancing, fun stories, and good jokes.