So here's is something that I consider one the most fascinating NXT creations of the last years: C5, the Flying NXT Blimp.
Two danish students, Lasse and Kenneth, created it for the LEGOWORLD Copenhagen 2011 where they managed to actually get it flying, controlling it remotely. They even attached a camera to it, shooting movies and photos from above:
You can get more details on their web site, BrickIt.dk.
Besides, the movie is also hosted on the official LEGO MINDSTORMS site.