i am fascinated by british tv shows now --- "coupling" --- best show ever. i laugh to tears when i watch any episode. i used to watch a lot of amercian tv shows. Top off my head, of course ,"friends", it's relatively easy to understand compared with other shows . "heroes", "two and a half men", "desperate housewives", "smallville", "one tree hill", "ugly betty", "the o.c", i also like "apprentice" ... oh my god, there are so many. :) in those shows about teenagers, or younger people, people speak faster, and that's good for practise listerning.

Seinfeld Friends The Simpsons Family Guy (those are full of references to american culture / stereotypes in a comical way)

"smallville" is a popular series and "friends".

agee, coupling is so funny.

I would not recommend comedy tv series - as often the dialogues are not realistic or else they rely on a knowledge of that culture to understand the humour. I think that dramas are the best way to learn English. (Before anyone comments that these shows are also unrealistic - I am only referring to the language used in them.) Crime shows such as CSI - while they may be interesting can have a lot of job specific language which may not be helpful in everyday life.