A whole new genre of search engines – for music. And the best part is that you can listen to the music on the site itself (even though the music does not reside on their servers).
Seeqpod, Songza and SkreemR are some examples. Both Seeqpod and Songza have neat interfaces and lets you play the files, which I think is pretty neat. Seeqpod allows you to even save your playlist and embed it in your site, like this one below.