7. E.R.
There are some shows that go from being a cultural icon to making people say, "Wait, that show's still on the air?" E.R. is a perfect example. A hit commodity in the mid to late 90s, E.R. went about its high drama medical business for fifteen years. Cast members that started the show and became famous because of it (George Clooney) moved on to their Hollywood careers, and were replaced by new recruits, who were in turn replaced by even newer folks. It's the television circle of life. To put it into perspective, kids who were starting kindergarten when E.R. began were almost through with college by the time it was cancelled. That's a long time in TV years. And while we can say that E.R. must have been doing something right to last for so long, a lot of it does feel like a decent show desperately clinging to its glory days.