I was trying to decide the other day what the best ever Christmas special of a sitcom was. It can't come to me. Here are some of my favourites:
Citizen Smith: A Story For Christmas
On the Buses: Christmas Duty
Only Fools and Horses: Christmas Crackers
Porridge: No Way Out
One Foot in the Grave: Who's Listening
Only When I Laugh: Away for Christmas
Incidently, you can't have Christmas Specials that have nothing to do with christmas, such as the classic One Foot in the Grave episode "One Foot in the Algarve", yes it was made for christmas, but christmas wasn't taking place in it.