For me its Only Fools and Horses and One Foot in the Grave....
Have seen every episode many many times but still if ever I switch on the tv and its on I will still watch the whole episode, though I must know every word!
I think I have hit a limit on only fools now, its taken a lot of years but I can finally switch it over, I hit the limit on the vicar of dibley some time ago, I think thats because there are not so many episodes
Gavin and Stacey, Flight of the Conchords, Summer Heights High, Family Guy, Alan Partridge, Big Bang Theory plus a couple of others. All of those I have on DVD and regularly have a little marathon day, even if I've seen them ten times already I love them still.
I've got all the Green Wing series and Christmas special on DVD and have watched them so many times, but they still make me laugh. (Scrubs was a very pathetic and disappointing imitation.)
I used to watch M*A*S*H every time it was on TV, even when it was shown with the dreaded laugh track, and subsequently bought every season on DVD; strangely, I haven't viewed a single episode since watching the final episode on the final disc.
Gavin & Stacey most definite! -I've watched them hundreds of times and never ever get tired of them! - I love love 'em!
Alot of the Fools & Horses, especially the later episodes
One Foot In The Grave
Alan ahh haaaaaa Partridge
Men Behaving Badly
The films - Shirley Valentine, Planes Trains & Automobiles and Pretty Woman