In the past we've covered the Mac application TV Shows, which automates starting bittorrents for tv show episodes. Sadly, it hasn't been updated in a while (though the main page still promises an update soon). However, I recently ran across another application that works in a similar way called ted.
With ted you can select various shows, even see summaries of episodes, then send the torrents off your your favorite bittorrent client (e.g. Transmission). Unfortunately, ted is a cross-platform java application, but it should run fine on any modern Mac.
ted is a free download from sourceforge.