eh? what happened to my reply?!
ah well, here it goes.
you could also use the little motors inside of a cell phone, probably easy and cheaper to get if you have some old cellies around. problem is though, what would you hook it up to? the games dont support it, and the only thing i see worth doing is hooking it up to the speakers so it pulses to the beat....
actually now that I think about it, hook that up with some sick tri-color sound reactive led's, while blasting some daft punk and you got a pretty portable rave!