The modern poster-child for a show that's "gone too soon" is Jericho. The impassioned fans buried CBS under a ton of nuts, which got the show renewed for a shortened second season. Your mileage of the quality of that season may vary, but the fact remains that the fans did something none of these internet campaigns today will be able to.

What people don't realize is that when Jericho came back for the second run, the ratings weren't any better than when the first season ended. So when they cancel your favorite show and you start mailing in bizarre objects and setting up your web petitions because "it worked for Jericho," remember that the networks remember Jericho as well. They remember that it failed to find a sizable audience twice.