Include comedies, dramas, whatever you like, and of any era. Here's mine:
1) Blackadder - one of the greatest and most consistent (first series aside) British comedies ever, along with "Fawlty Towers".
2) Twin Peaks - innovative and scary - like nothing else I have seen on TV, before or since.
3) Law and Order: SVU - yes, the subject matter is often grisly, but some of the best crime writing going around, all squeezed into such an efficient format.
4) Doctor Who - cardboard sets, a great blend between scifi and fantasy, and a long, rich history. Apparently gonna hit our screens again with a new doctor in '05.
5) Seinfeld - one of those shows you either get or you don't, but I think most people do. Frequently hilariously funny and one of the greatest implementations of situational comedy ever.