Spotify also has pretty good recommendations, but requires people to be authenticated to use their recommendations API. Our recommendations currently come from Last.fm.
i.e. if I search for an artist and press play on one of their tracks and let the stream keep playing it goes onto other tracks by that artist, but is there a way to get it to add related tracks too? Like the old last.fm artist radios.
edit: it's now doing that for me so maybe there was just something weird about the recommendations set earlier. Unfortunately I searched for some chilled out electronic stuff and the recommendations are all aggressive hip hop but that's not your fault I guess...