This might get passed off as something for people looking do to evil/illegal/etc projects, but Gazelle is easily the best tracker front-end out there and it's super customizable (google "Gazelle tracker" and you'll likely find a bunch of screenshots of different sites implementing it differently—from skinning it to adding new features). Bittorrent is underused as a medium for legal downloads and I encourage anyone interested in a torrent site of any kind to check this out before they try to write their own.