Napster. I forget how much a subscription is. I just pay 99 cents a song, but there is some kind of option for subscription. I actually like it more than the old "illegal" Napster because you always get the real version of the song. No worrying about getting some weird version of the song or the first verse keeps repeating.
I really like iTunes. Granted, I got it for free w/my mini iPod, but you can download it off the apple website even if you don't have an ipod. I really like it - it's fast and I like the features.