Have you heard of the Chapman Stick? It's an electric guitar-ish instrument designed specifically for tapping.
Never heard of it. Got a link?
It's a very neat concept. I wouldn't mind learning to play it, but they're shockingly expensive, and obscure enough that I doubt there are many resources for learning. They're very cool, though.EDIT: Here's another good one:
EDIT: Here's another good one: