I don't know if you consider these secondary characters but in "Identity Crisis" and "Catch Me If You Can," I like the reaction Columbo has to the belly dancer's. It's amusing.
Something that slightly bothers me is when Bruce Kirby plays a background character in one episode like the lab attendant in 'Lovely but Lethal' but then plays a Police Sgt. in another episode.
I agree with you Mark, Bruce Kirby also played a television repairman in "Make Me A Perfect Murder."