The Freesound Project is a collaborative database of Creative Commons licensed sounds.

This is a community music site featuring remixes licensed under Creative Commons, where you can listen to, sample, mash-up, or interact with music in whatever way you want.

A search engine for copyright free music loops.

PolyPhontics GB is a software instrument toolbox made specifically for Apple's GarageBand. Sporting some of the same features as its big brother, PolyPhontics, PolyPhontics GB gives you the tools that you need to create software instruments for use in GarageBand compositions.