The Amazon Web Services Blog reveals a simple search syntax to turn Google into your own personal (free) Napster:
-inurl:(htm|html|php) intitle:”index of” +”last modified” +”parent directory” +description +size +(wma|mp3) “Nirvana”
Just replace Nirvana with a song or artist of your choice to display a results page of indexes that contain downloadable MP3s.
P.S. Don’t steal music.
In the comments, JLOCK84 adds:
The folks from I-hacked made a little site that does this for you, G2P.org. Finds music files, as well as ebooks, and can also work as a proxy.