Also try SkreemR (http://skreemr.com/), another playable music search (with some other cool features). The Tech-Reicipes Blog has a good description of the coolest features.
Try out SeeqPod (http://www.seeqpod.com).
It's a new search engine that searches the web for playable MP3 songs and then lets you play them right on the web page.
It's a great way to find free MP3 music, and it's arguably legal! :)