Napster. You may remember Napster from their classic courtroom battles involving Metallica, and in particular, Metallica's highly irritating drummer Lars Ulrich. Napster has changed quite a bit since then, with the most critical change being that the company is now legit. Not 100% sure how there system works, but I do know that they are currently offering free 7 day trials.
Napster 7-day Free Trial with Unlimited Access to 3 million+ songs in CD quality sound.

At the moment it looks like it's only valid for US users, but maybe that'll change in the future. Worth keeping an eye on.