I have a constantly running server that would be a perfect on which to run torrent downloads. The only catch is that the server is headless -- it has no monitor or keyboard. To overcome this obstacle, I use rTorrent as my torrent client, and GNU Screen so that I can disconnect my terminal session and leave rTorrent running.
rTorrent is a full-featured BitTorrent client that was built to run on a terminal. It uses ncurses as an interface layer and libTorrent under the hood. rTorrent is in the package repositories for most major distributions. If it is not available on your system you can download and install from source.