The networks will keep cancelling TV shows just as surely as they'll keep introducing new ones. Below is the list of TV series that will or have ended during the 2012-13 season. In short, they won't be back for 2013-14.
This list will be updated as the season progresses so feel free to bookmark and check back.
If you believe a show has been cancelled and don't see it here, you can check the 2011-12 and 2010-11 lists.
Update: You can now check out the 2013-14 list!
30 Rock (NBC)