Where is Last.FM on this list? It's actually the best (in my opinion) service out there. Their "discovery" feature is the best, and simplest to use - just choose "Play artist/song/tag XXX radio", and it will play related songs for you. Their catalog seems immense, and I listen to some of the most obscure stuff out there (/hipster joke). And it's completely free.. the only thing it doesn't do is play music "on demand", but nobody else got that right either (for free).
"This article compares services that provide access to interactive, on-demand, and complete music playback, whether paid or free. So services like Pandora, Last.fm's radio, iTunes music store, etc, are not considered because they technically do not satisfy the criteria."
While I agree that last.fm is pretty great, there's a reason it was not included in this list.
