Via the lessig blog:
This is easily the coolest technology I’ve seen in years: Go to the Creative Commons search page. Click on the OWL Music Search tab. (Depending upon the browser, you might need to run a fake search to get it to come alive — we’re working on this, but just type anything in the search bar). You’ll then see OWL’s Music Search interface. Drop an MP3 on OWL. It will analyze it and show you similar sounding Creative Commons licensed music. You select the part of the song you want to match; it finds the closest match it can find.