This is a list about TV shows that made a difference... changed the world, or America... changed culture... changed the way we talked, thought and (mostly) watched.
Changed you. Changed me. This is not some sort of thing TV Guide or Entertainment Weekly puts out -- the best, the brightest, the most wonderful, most popular etc. Some of these shows may be, in fact, demonstrably not very good -- though in most cases, they are very good.
Another proviso: I set aside most news programs. Of course they were influential ("Evening News," "Meet the Press," "CBS Sunday Morning," "SportsCenter," "Nightline," and so on). "Today" and "Good Morning America" are on this list only because they are pan-cultural -- not simply news, but simply everything.
As I put this list together, here was the common denominator: Impact. In each case, this show might have spawned other similar shows, or even spawned an entire genre, or movies, or lingo, or fashion. The show had deep tentacles into popular culture, and to an extent, still does. The show had "stickiness" -- no matter how hard we tried, we just couldn't forget. It was like a song that looped continuously through our imagination -- the lower or higher reaches of our imagination.
So please, do get mad if your favorite show isn't on this list. But I would bet it is.