Allofmp3 is an online music store, but it's so cheap that it might as well be free. You pay by the gigabyte; 1 gigabyte costs $10. That means that 10 bucks gets you about 18 hours of music (at 128 kbps Ogg Vorbis -- more than good enough quality for me, YMMV). It doesn't get cheaper than that.

It's a Russian company so you may not trust them, but you don't have to -- you can charge your account using PayPal, so they don't ever get any personal data from you other than your email address.

They have a huge selection of mainstream and non-mainstream stuff, about 200,000 songs in total. And the best thing - it's not illegal. (This is not so much important from a moral but from a practical standpoint - they can provide reliable high speed access to the goods.) They have a licensing agreement with the Russian Organization for Multimedia and Digital Systems which allows them to sell these songs in bulk; the same kind of agreement Russian radio stations have. Read the whole article