Hey Brian - have you looked at emusic.com? They don't have everything, but their selection of not-so-famous artists is reasonable. They do have Martha and the Muffins and Tarika Sammy, for example. But none of your others. They're really not good at all for actually famous artists like Led Zeppelin. Some of the albums are limited to 128kbps, but lots are much higher VBR.

Anyway - in terms of access to some obscure-ish music, they do have a decent bit. There are also no restrictions on the files - copy and burn as much as you want. And hey, it works on Mac and Linux, too! It might not fit the bill for you entirely, but it's better than Napster for lesser known artists.