Do you have a few legos lying around?
Then build a working Harpsicord: http://www.henrylim.org/Harpsichord.html

Man, that's cool. Beats the hell out of the mini piano James Earnest of Cheapass Games built. That one had moving counterweighted keys, but didn't play any notes. Picture of it is no longer on the site. Bummer.

Wow, somone had a little time on his hands.