Libble.com is one of the first ratio free music trackers to hit the BitTorrent scene. In my opinion this is a very underrated tracker –it has a great set of usability features (runs on Gazelle codebase), a content rich torrent index and a decent user base. Keep in mind that Libble is a private community and public registrations are currently closed. However there is some good news for those who are itching to get in - free invites are available on the official IRC channel.