The killer is usually a kind of "foil" for Columbo without being funny in an OBVIOUS way, but a few have been exceptions to that. The two obvious ones I can name are Abigail Mitchell and Nelson Brenner, though there are certainly others. In spite of the murders, Rodger Stanford is a kind of "big kid," so I guess he'd be another one.
When it comes to ones who are funny but NOT in the most direct way, there are a lot more, like Paul Galesko and Paul Hanlon. But one very big one is Jarvis Goodland, partly because Ray Milland was so great at playing "superior" characters, so of course he clashed with Columbo in an extra big way.
Agreed, and to that list I would add William Shatner, especially in "Fade In to Murder," in those hypothetical conversations where Shatner speaks as his fictional detective character analyzing his own crime, and at the end, when he laments, "Lieutenant, you would do me a very great favor if you stop calling me SIR."
Speaking of dry wit, Leslie Williams has it.
Columbo: "My wife says to me, 'You can really be a pain.' You know what I mean?"
Leslie: "I get the general picture."
I know that I’m combining characters, but Jack Cassidy had some great lines which may even have been ad-libbed. In Publish or Perish, after Columbo tells Riley Greenleaf that “this man is a locksmith”, Greenleaf sarcastically replies: “Hooray”.
I also love the line in Murder By The Book when Columbo says: “I was in the neighborhood” and Ken Franklin replies: “You’re always in the neighborhood!” He also tells Columbo to continue his theory “as boring as it is”.