Sorry to bump up this up, but I missed posting in this when it was recently bumped, and I'd like to post some of my favourites. I'm not a religious fanatic of television as many here, yet there are things that I really enjoy. Such as...
The Simpsons
I'm not sure if this will class as a sitcom, being a cartoon and all, yet I think that I have to say that this is my all time favourite TV show. I like the cynical attitude of it, especially the episodes where the Simpsons visit other countries. I am not a huge fan of it as I used to be (five or six years ago the only videos that I ever bought/rented were Simpsons videos), yet I still enjoy it thoroughly whenever it is on. And I still need to get those season box sets.
Friends
I actually only started to get into this really when the last series came on (I used to find it rather overrated), and I'm finding it more and more entertaining on each re-run I see, even if everything isn't completely hilarious.
Little Britain
This is more a sketch show than a sitcom, yet repeated characters appear. I believe that it's got a cult following in America, but in Britain, it's even bigger (the DVD was a sell out and I'm probably the only person here that doesn't have it yet

), and it's no wonder, as this is a surreal laughter maker.
Goodness Gracious Me
Like
Little Britain, this is a sketch show parodicising aspects of Britain, only this focusses on the aspect of Asian culture in Britain (I should point out as well that this was made by Asian writers/comedians). It worked, as the comedy was broad enough to break out to a wider audience, such as inverting aspects of Anglo Asian culture (Indian students finding their soul on a back packing gap year to England, for example). I have the video set of the first series (which I bought a few weeks before discovering we were going to get a DVD player

) and I remember watching it in one go a while ago. Great stuff.
Various Warner Brothers and Disney cartoon series from the late 1980s and early 1990s
I have fond memories of watching Disney things like
The New Adventures of Winnie the Pooh, Chip and Dale: Rescue Rangers and
Duck Tales to Warner's
Tazmania, Tiny Toon Adventures and
Animaniacs. Though with some of those things I haven't seen them in years, I think that they'll hold up for sentimental value.
I also enjoy a few other things like
Will and Grace and
Keeping Up Appearances, though I think that I don't watch/know them enough to put them in my favourites list.