Here are some links that may help you all in crafting your tunes.

http://www.grsites.com/sounds/
http://www.a1freesoundeffects.com/
http://www.bangin-beats.com/freedemos.html
http://ccmixter.org/
http://freesound.iua.upf.edu/index.php

I'll post more links as I find them. Feel free to add your own as well.

p.e.a.c.e.