There are some great ones in here. I'm a banjo player, and I'm looking forward to telling some of these at my next gig. (No, it won't be New Year's Eve, and I didn't leave my stuff there...)
Here's one I heard Michael Cooney tell at the Philadelphia Folk Festival a few years ago:
A guy is browsing in an antique store and finds himself extraordinarily drawn to a brass figure of a rat standing erect.He buys the statuette and walks out with it. He sits down to examine his treasure and notices that there's a hole in the back of the head; he looks some more and sees more holes running down the front. He blows in the top hole and finds he can play it like a flute.
He plays a bit and then gets a start when he notices that a rat has emerged from a hole and is intently listening. As soon as he stops playing, the rat disappears. The guy walks away, then starts playing again--and another rat materializes.
The guy has it figured out--he keeps playing and walks out of town toward the river with a multitude of rats following him. He leads them into the river, where they all drown.
He goes back to the antique store and asks the owner: "Got any of these in the shape of a banjo player?"