Philip Verbeek has sent us through version 4 of his Great Ball Contraption. We've shown version 2 before and this one follows in a similar style. With 7 separate 'modules' its impressive, but what truly makes it stand apart is the fact that the whole thing is powered by a single motor. There is a great implementation of a Geneva Drive towards the end of the video which is worth sticking around for.
As an added bonus, the NXT uses a light sensor to keep track of how many balls have passed through :)
**Update** Here is version 3 :) - http://www.youtube.com/watch?v=slVg6G33taA