When I saw Scribblenauts on E3 coverage my thought was immediately:

I want to stop everything I'm doing and make a game quite like this, but for the iPhone or Flash and allow anyone to make things for it (like a wiktionary of 2d "mobs" and items).

The video I liked most was: http://revision3.com/coop/showfloor/#seek=636:839

Of course, I've got too much on my plate to do that right now, so maybe someone else will. :)