Like Bruno said, Archive.org is the best. Especially if you are like me and can't get enough Dead. I'm listening to a nice Grateful Dead show as I type now from archive.org.
Nugs.net is also good like gov't mule said. But with a screen name like that, what would you expect? Unfortunatley, not enough gov't mule available. Gotta love Warren!
If you are into the grateful dead, gdlive.com has some stuff that you might not find on other sites.
Don't forget about friends too. I have thousands of songs that I downloaded from friends and never worried about the cyber police knocking at my door for stealing music.