"Goombah is a free service that helps you find new music and people who share your musical taste whether you're into blues, alternative, classic rock or any mix at all. Based on your iTunes collection and listening behavior, Goombah displays like-minded members' collections and recommends tracks they really like that you don't have. You can show your friends your music collection, and explore matching members' and friends' collections. Goombah also suggests free tracks for you to download based on your taste. Or browse our Free Music collection of legal, professionally produced music and come back every week for "Free Music Friday". With nearly five million unique tracks in our members' collections and growing, your recommendations, matching members and free music are constantly changing."This looks like a great service for all you iTunes users. It scans through your entire library and recommends songs to you. It looks like collaborative filtering more than an anlysis of the actual musical frequencies, or some or technical stuff, but still, it seems to be very easy to use. There is
more information about the service here, where they show screenshots and give a more detailed list of features.