Top five:
Doctor Who (roughly 1963 - 1979)
I, Claudius
Monty Python's Flying Circus
Honourable runners up:
The Strange World of Gurney Slade (early 1960s Expressionist TV drama - from the days when television was experimental)
The Avengers This is the '60s spy TV series, not the recent movie, and has nothing to do with comics. Two of the seasons (Mrs. Gale, b/w Mrs. Peel) are brilliant, but the other episodes vary in quality from worthy but dull, to formulaic murders of civil servants, to Op Art mishmashes.
The Prisoner "I am not a number, I am a free man!"
Not Only, But Also - Peter Cook & Dudley Moore
Blackadder
Coupling Not for the rom-com, but for the way in which Moffat plays with the structure of episodes: the same five minutes seen from different perspectives; episodes in split-screen.
Jeremy Brett Sherlock Holmes
Poirot
I'm watching The Mysterious Cities of Gold at the moment, which is a children's cartoon, but one of the best programs I've seen, regardless of age and genre. Each episode ends with a short documentary; I suspect this is where I got my interest in archaeology and Mesoamerica from.