We've shown off a lot of these GBCs (Great Ball Contraption) in the past, but they never cease to amaze me. I love how the very simple idea of moving a LEGO ball from Point A to Point B can result in so many amazing creations and mechanisms.
This one was put together at the recent LEGO world 2012 in Zwolle (of which a few theNXTsetp contributors managed to attend). It's 15 minutes long, but if you're anything like me, you'll find that time fly by.
Not every section is NXT powered, but see if you spot those that are.
What's your favourite module? I personally love the pneumatic 'worms's at 8 minutes, the 'pickers' at 10:15
For the technical details about how to create your own module, check out Steve Hassenplug's page - http://www.teamhassenplug.org/GBC/