If you use KDE as your primary desktop then you can try qBittorrent or Ktorrent for instance. But one of the good things about this utility is, if you want a GUI that can be downloaded in both Qt and GTK+ tool-kits, then Transmission is an elegant application.
Unlike few other "free" applications, Transmission does not come with annoying ads or anything like that in nature. You can manually set uploading/download speeds, downloading folder, enable/disable protocol encryption, Port forwarding, track editing/updating, etc are few of its main features to mention.
If you use Ubuntu 11.04 Natty Narwhal (should work for other versions as well), then you can install Transmission 2.31 by entering the below command in your Terminal window.
sudo add-apt-repository ppa:transmissionbt/ppa
sudo apt-get update
sudo apt-get install transmission