I can only envy those who have never seen an episode of Seinfeld, when I think of the pleasure that they have to come in their lives. I would recommend wholeheartedly the brilliant DVD of the first three series which came out in time for Christmas. Not only is it the perfect introduction to the greatest ever sitcom, but it is the best packaged DVD I have ever come across. It suits both aficianados and those who have never seen a minute of it.
Frasier was great in its time too (probably series 2 to 5). It seriously jumped the shark when Niles and Daphne go together (sorry to spoil it for you, MFJ. ).