Not in any particular order:www.iuma.com (Rules!)
www.vitaminic.com (Acquired iuma, but is itself not that great.)
www.efolkmusic.com (Not a bad little place.)
www.musicbuilder.com (Offers mp3 CDs as well.)
music.lycos.com (I think that's the addy. They aren't that great anyway.)
www.avantnoise.com (Rules! Also has mp3 CD capability.)
www.farmclub.com (Which is being merged with something, so don't put your stuff there.)
Unrated:
That's all that I know of so far.