The Radio Times has published a list of the top 25 TV put downs ever..
The list contains (perhaps predictably) a lot of BBC shows, but some classics none the less.
Mind you, I think my personal favourite is from Statler and Waldorf (the old guys on The Muppet Show):
Statler: "Wake up, you old fool, you slept through the show."
Waldorf: "Who's a fool? You watched it."
Another favourite from Red Dwarf (although I am not sure whether it's from the TV series or books):
Rimmer is giving a speech, Lister is in the audience.
Rimmer: Lister! There's always one isn't there?
Lister: Yeah, but he's not normally the one giving the speech.