There are a number of network tv shows that could do a lot better if they were under a premium network and didn't have their hands tied, storywise.
Someone already mentioned Revolution, which was the first thing I thought of. So I'll go with another one that came out around the same time that seriously needed to be somewhere where it could be more mature; Under the Dome.
The one that sticks out to me the most is not a TV show, but the two adaptations of the "The Stand". That should never have been produced by a network. It needed the freedom to go dark when necessary.