I like Emusic, but it definitely appeals to a certain kind of music fan. If you're looking for Coldplay, Kanye, or Fall Out Boy...or basically anything else that's played on the radio...you're not gonna find it here.
If you're looking for independent, self-released, or under-the-radar kind of stuff you'll get a lot of music for your dollar at Emusic. I get 65 mp3's a month for about $15, and it's just not enough...I'm considering upgrading to the next plan.