SoundShelf.com hosts free music of various genres and makes it all available under the EFF Open Audio License, or a Creative Commons license. This was taken directly from their FAQ:
2. When is free music legal?
Free music is legal when the artists want it to be. Until recently it was near impossible to know the artist's feelings and intentions as all works were automatically copyrighted. Today with the emergence of the Creative Commons License and the EFF Open Audio License the artist's desired intentions are expressed by the license that they choose to publish their works under.