Jamendo, a music site for truly independent artists. The selections veer away from mainstream music industry fare. I particularly appreciate the offerings under Latin, Blues, and Electro. My favorite so far is La Caja Negra, a Spanish group that plays both Latin and Rock.
The site doesn't just offer individual tracks but complete albums. They come in both MP3 and Ogg Vorbis formats. They're all legal, too: Jamendo works on a system of voluntary donations.
You can also use Rhythmbox to stream music from Jamendo.