i think there was a thread on mp3 blogs a while ago. some sites were listed there. it's hard to keep up, new ones keep popping up. but here is a big list of them.
http://tofuhut.blogspot.com/2005/05/...-here-you.html
for other types of downloading sites....
subpop has a weekly single on itunes, i think. i signed up for the podcast a while back.
kind of a roundabout way to getting mp3s, but it works
http://www.subpop.com/multimedia/freeradiosp.php
i used to check out epitonic
http://epitonic.com/