Separamos alguns sites que possuem musicas em  MP3 para downloads grátis veja:

BeeMP3.com
Blip
Critical Metrics
Deezer
Free Albums Galore
Free Music Zilla
GrooveShark Lite
Hype Machine
Imeem
Jango
Last.fm
Musicovery
Music Search Online
MuxTape
Pandora
SeeqPod
SpiralFrog
Skreemr
Slacker
Songerize
Songza
Bis
4Shared
2Shared