Head over to Pandora.com for free, high-quality streaming music, in playlists that cater to your personal taste. I've been using it for over a year now, and it makes for an awesome WoW soundtrack to play to... especially during vent QQ sessions. =)
It's pretty simple to use. All you do is tell the player what bands you like, and it'll find similar bands for you, play their songs, and you get to rate their songs as either a "thumbs up" or a "thumbs down." Simple, but works amazingly well at finding new music you may actually like. Hopefully you find it worthwhile. I do.