Any tv series were they do basically the same thing over and over qualifies as filler. Eventually MASH stopped being original and they knew they had to kill it off.

Shows like Friends and Threes Company are ALL filler. They never have one original idea. You're just watching a group of people you like either sitting around and doing nothing, or getting up going outside and doing..... nothing.

Critics whined that Seinfeld was a show about nothing. But if you ACTUALLY PAID ATTENTION you would have noticed in every single episode they are doing something. And its something different each time. And that made it a hell of a lot better than most sitcoms up to that point.