Hard to pick just one. I was addicted to "X-Files" and "Northern Exposure" for a long time.
And I loved Carl Sagan's "Cosmos" as a kid (I know, how geeky is that?!!). :doh:
In recent years, "Sex and the City" and "Sopranos" were favorites. I was slow to come to "Seinfeld" but it really grew on me.