For me, most important is that music is DRM-free (DRM= "Digital Rights Managment" = Copy Protection) and fair.
Such portals are:
www.bleep.com
www.finetunes.net
www.akuma.de
(10€ for an album, that's OK IMHO.)
If you don't want to pay anything, check out some of the netlabels. A good place to start is
http://www.de-bug.de/pod/
if modern electronic is not interesting for you and you still don't want to pay anything, you can check the out of print blogs. Ah good place to start is
www.weirdomusic.com
And if you really miss allofmp3, you can check
www.mp3spy.ru
but i really don't recommend that.
Instead of paying there, you could as well use a P2P platform, it's not more or less unfair regarding the artists.