When into Techno, DNB and stuff like that I found the Newgrounds Audio Portal to be a good source (ParagonX9 etc.). It of course features other genres too...
Remixed game music. Third party usability probably is questionable...
PD music, mostly instrumental.
- lots of CC-by-SA, -NC and what not. You have to check the particular licensing though, since almost every possible CC license is covered.
French site featuring free albums & songs.
Lots of free music from various genres and artists.
Music by Kevin MacLeod covering various genres.
Music from different gernes and artists.
Yet another site for music under the Creative Commons license.
(Metal) music by Marc Pullen.
An excellent resource site would be Freesound.org which features tons of sounds. Other sources would be: