Sickbeard
Sickbeard is advertised as "The ultimate PVR application that searches for and manages your TV shows - Automatically finds new and old episodes for you and it works with your current download client!" This is exactly the type of thing that computers were designed for! Tivo and the cable companies have offered pay upgradable DVR receivers for many years now, it seemed crazy that the internet didn't have a similar feature to offer all of you perfectly legal file sharing types...
Before we get into the installation and configuration portion of Sickbeard let me talk for a brief moment about the pitfalls you may encounter.
When I began using Sickbeard I already had a robust library of episodes. Not the type of library that was easily repaired or replaced after making a mistake with a program that would automatically rename and sort my files...
Trust me when I say, "It sucks when you accidentally destroy and entire show's worth of data just by scrambling all of the filenames. It sucks so, so much."
Okay, there are a few keys to making Sickbeard work well. The first is understanding what each post processing option does, and the other is strict German-esq folder organization.