iTunes, Rapsody, Napster 2.0, MusicMatch, and whatever other pay music download services at out there.
I'm here to tell you that they all suck horribly.
I've just started using the kick-ass allofmp3.com, a Russian music site that gets you your music at an incredibly cheap price. just $.01 per megabyte! Basically it’s like this, you pick the song you want, then you get to pick the file type (Mp3,AAC,OGG, or WMA) and then the quality, and whatever the final size of the song is you pay $.01 per meg. So I get a song with NO DRM, encoded at 320kbps for $.12, whereas someone using iTunes pays $.99 for the same song encoded much lower. Their music catalog is huge too! I'm only put down $5.00 and I've downloaded two whole albums at 320kbps! I'm in heaven!