Lost
Seinfeld
Medium
The X-Files
24
Heroes
Twin Peaks
Not one of those shows would make my top 100.
YMMV.
Of course, I've watched less than two hours of television in the past two and a half years, so perhaps my opinion is not entirely valid.
I do remember a few shows that I liked...
Firefly
The West Wing
Joan of Arcadia
The Paper Chase*

Buffy
and a few non-drama shows from the Discovery Channel or PBS.
Can't think of anything else, maybe that's why I don't watch TV anymore.
Hmmm... I do see a bit of a common thread among the ones I liked: interesting and deep character development, where every episode wasn't all about the same central character every time...
tanstaafl.
*Nobody under the age of 40 is likely to remember this very memorable show.