About two years ago, a guy posted a how-to for turning old NES cartridges into a harmonica. If you lack the tools, know-how, or NES carts to make one yourself, someone's now selling them, for $24.99.
I don't know if the seller is the same guy, and I'm not saying someone took another's idea. All I am saying is, two years later and fully in the throes of the global recession, harmonicas are definitely a top-trending musical instrument. And everyone who wants to can hum a few bars of of the Top Gun anthem or the Super Mario Bros. theme - using those games. And that's awesome.
Update: The original harmonica's creator contacted Kotaku to say he's not the one selling it, but he seems to be alright with this. "Posts like this are really more than I'd ever hoped for, especially two years on. Still haven't learned to properly play the damn thing, either."
NES Harmonica [Makers Market, thanks Ryan]