I recently decided to go legit with my music collection, so I started getting free downloads at music.download.com, garageband.com--not the Mac GarageBand, live music archive at Internet Archive, some Irritable Colon--this links to their server, whose URL one of the artists gave me, and Etree (although I've only used their BitTorrent service to get one Dave Matthews Band recording so far).

You can usually find a few big-name artists on these sites (especially the live recording ones, which are totally legit), but it's also fun discovering new stuff.

Happy hunting.