Kinda strange that neither NBC nor ABC ever set Columbo against a stand-up comedian. You'd have the dichotomy of comedic humor and anger, sizzling one-liner dialogue, the whole chaotic nightclub/stage milieu, and a great climax as Columbo plays heckler/interrogator to villain Rickles (or Newhart or Carlin or Gorshin or whoever).
Charles Nelson Reilly would have made a terrific sharp-tongued but slimy heir out to fleece the family fortune, while '70s Betty White could have had a ball playing a variation of her Sue Ann Nivens character from Mary Tyler Moore. Bob Newhart vs. Peter Falk -- now THAT would have been classic. OR if you wanted to get all '70s topical, picture George Carlin as an Abbie Hoffman-type going up against Columbo.
And I know Dawidziak declared him as the anti-Columbo villain, but I think Sammy Davis Jr. would have been great riffing hiply off the Lieutenant.
Since you mentioned MURDER BY DEATH, I would have loved to have seen Peter Sellers as a killer. And on the far out wacky end of the spectrum, how about Paul Lynde?
Roscoe Lee Browne (who of course played the psychiatrist in REST IN PEACE, MRS. COLUMBO) would've been great as one of those very refined killers with a snobbish way about them. The Ray Milland kind.
He had a real knack for playing funny authority figures, so he could've played an authority figure (one who didn't happen to be the killer or the victim, so they could afford to make him funny), in some episode about big business.