Deluge is a feature rich bit torrent client, which is really popular among Linux users. Deluge is cross platform and works in OS X, Unix and Windows platforms as well. Though I would rate KDE's KTorrent over Deluge, Deluge is definitely well integrated into the Ubuntu's Gnome desktop. Deluge recently released the first release candidate of Deluge 1.3 series packed with a lot of new features and bug fixes.