Somehow I can never think of that many.
MYSTERY SCIENCE THEATER had only one that I can ever think of (which is surprising, since it's so full of pop culture jokes), in the "Incredibly Strange Creatures" episode.
This isn't actually about a TV show.
I think someone posted it some time ago, but there's the Columbo appearance on the Burns and Schreiber album "The Watergate Comedy Hour."
I just realized the actor that played Niles in that clip from the Nanny was in a Columbo episode. I just looked it up, but i'll let you curious Columbo fans see if you know?