When I first got my MacBook I installed Transmission to look after my BitTorrent downloads but found it a little too lightweight for what I wanted. Bit Sticks has to get an honorable mention as a cool widget for for downloading torrents. Runner up was BitRocket but the top podium spot has to go to Xtorrent.
Xtorrent is made by the same team as the Inquisitor plugin for Safari. It is feature rich with a great search tool, organisation features and iTunes integration. Now if it would only hurry up and download my Ubuntu image for Parallels.