I would actually use Audio-Galaxy Satellite P2P again to find new music.

Had one of the best artist recommendation algorithms ever.

For your local music library tastes, it would first crossmatch to find other users who had the most similarity to your collection, then recommend you the artists that they had, that you didn't.

Simple and elegant.

* As mentioned elsewhere, Nicotine/Soulseek is the modern leader for recommendations.