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.

Soundsnap is the best platform to find and share free sound effects and loops- legally. It is a collection of original sounds made or recorded by its users, and not songs or sound FX found on commercial libraries or sample CD's.