Enders Game by Orson Scott Card. I heard a few years ago that they were going to make a movie of it, but nothing's ever come from it. It would make an amazing movie. I'd love to see the Tales of Alvin Maker series made into a movie, too, but it would probably be a bit too weird and spiritual to get much interest.
The Sky O'Malley series by Bertrice Small. Any of her books really. Nobody wants to make historical romance novels into movies, but her books are just amazing.