i'm being predictable but...
but depending on your definition of GOOD music, the cheapest way to go is emusic.com... the cost per track is about a third of what the itunes store costs. plus you get drm less high quality mp3s.
if you are looking for mainstream major label songs, than emusic is not for you. if you are looking for indie stuff, like YepRoc, Epiteth, 4AD, Beggars Banquet, Parasol, Kill Rock Stars, etc.. then emusic is way to go... PM and I can hook you with some free trial tracks.