The Music Recommendation System is an automated system that provides music recommendations specifically tailored to each user to find new music that they might like. This system, designed by students at the University of Illinois (Champaign-Urbana), operates by taking ratings from your own iTunes playlists and comparing them against other users who have used the recommendation system. Right now, the creators not that they have a very small number of users, and so the recommendations will most likely be laughable. However they will get better over time as more people enter into the system; meanwhile, enjoy while the numbers grow.
The Music Recommendation System client software is available for Mac OS X and Windows.
More info and download link here.