I can think of a few, so let me start:
1) I personally hope they make a 3rd movie in the Ace Ventura saga. Seriously, tons of old movies (Like men in black) eventually became a trilogy, and if anything should become a trilogy, I put my hopes in Ace Ventura. I am a big Jim Carrey fan, and he's getting old! I think he can do one more comedy movie and seal his legacy, and being the pet detective one more time would make me a happy camper.
2) A prequel to the Matrix trilogy. And no, I do not want any other sequels, just a prequel. It would be based off the War between man and the machines. I know they made the Animatrix and the "second renaissance", imagine how dark a movie that would be? The matrix is one of those few movies that pulls me in and makes me feel like I'm in such a dark reality, it would be great (no Keanu Reeves please).
3) Air Bud meets UFC. Need I say more? LOL