I've recently discovered the KDE audio player amaroK (which, by the way, is the freaking business - I won't reiterate why) . One of amaroK's features is integration with audioscrobbler, a music database. In short, amaroK can send your currently-playing track to the audioscrobbler database, and using that data combined with that of others, can link you to other artists/songs that you might like.

The whole thing sounds a little wierd on the privacy side of things, but their website appears to have a decent privacy policy, and the anonymous data is available under a creative commons licence (neat!).

Oh, and here's what I like.