All time favourite: M*A*S*H
The serious backdrop, the satire, how they blend comedy with something serious and grim, probably the only sit-com I ever saw that makes one think.
Another favourite: The Prisoner.
James Bond on acid. It has that surrealism that totally won me over.
Then of course the first 2 Black Adder series. Monty Python's Flying Circus too although that's less of a series and more of a sketch show.