Some great choices there: Donald Pleasence, Ricardo Montalban & Jack Cassidy.
I have to add a couple of my own faves:
Identity Crisis (1976) starring Patrick McGoohan & Leslie Nielsen. Also featuring Paul Gleason (Clarence Beeks from Trading Places).
By Dawn's Early Light (1974) also...
I was just going to say that I also love Quincy ME but you don't see it on tv much any more. I never really watched Diagnosis Murder so I can't give much of an opinion but the cast is very high quality too.
Just watching some Columbo on 5USA, I got to thinking if this question or similar had ever been posted. I know plenty of Vera / Morse lovers but I have to say I'm a bit of a Columbo nut.
Columbo isn't a "whodunnit", it's a "howcatchem". The joke being, your nan pipes up an hour in with "I...