1. TRON, definitely. If any movie made sense in either Tomorrowland or Future World, this is the one. This could be absolutely mind-blowing, with state-of-the-art 3-D computer effects, realistic audio-animatronics, etc. I'm talking Spider-Man plus here, with a completely immersive environment starting out with a deres-ing sequence moving you from the real world into the game world.
2. The Nightmare Before Christmas - Often discussed on these boards, I love the idea of an attraction devoted to this movie. Haunted Mansion Holiday at Disneyland has proved just how good and popular this could be. The Studios could use a great E-ticket, and I think done right, this might work.
3. Monster, Inc. - A GOOD attraction dedicated to this movie. It would be a roller-coaster style attraction which could weave in and out of Monstropolis, the door storage areas, and the real world.
4. Aladdin - Again, a GOOD attraction dedicated to the movie. This time, we're talking a wild ride controlled by the Genie (since this is my fantasy, Robin Williams WILL do the voice). Since he's unpredictable, there would be different sections he could send you to each time you ride. One time you might end up trying to escape from the Cave of Wonders. Another time you might have to go up against Jafar, another time you'll race through the streets of Agrabah, and so forth. It might require a lot of space, but since it's different all the time (there could even be different things that might happen within the plotline the Genie throws you into) it would have a great re-ridability factor.
And to wbt06, I think Bedknobs and Broomsticks is better known than you might believe. It's on TV pretty frequently (it was on Hallmark just a few days ago) and it has been released on DVD a couple of times. I think it might make a great attraction, too, especially with the idea of the bed jumping from location to location, allowing someone to "start" the attraction by twisting the bedknob and saying the magic words, and the great music. This could be a tour-de-force of Audio-Animatronics, rivalling Splash Mountain.