30 Rock. Watching it right now.
If you like spy-type stuff....I would strongly suggest MI-5. It is British, but I really enjoyed it. Unlike most shows, it was not afraid to kill off its main characters.....often.
Also, on the Sci-Fi side, Firefly is a must, even though it was only one season. After you watch the series, then watch the movie Serenity. Especially if you are a Summer Glau fan. I also liked Farscape....has some of the SG actors in it.
The net Battle Star Galactics became one of my all time favorite shows from Netflix. Interesting look at the human race. (and I'm not a big Sci Fi fan)
Firefly was good, some of the episodes annoyed me, but I found myself liking it more as time went on. Great cast.
Dexter is great, but they only have 2 seasons.
Arrested Development is great, but it's short, Breaking is awesome.
Blue Mountain State
If you like nerd shows, The IT Crowd is great. Brits crack me up.
Another vote for Breaking Bad. I've been watching it on Netflix lately and am only about halfway through season 2, but it is probably the best first 2 seasons of any show I've seen.
If you want a funny show, they don't get better than Arrested Development.
The Walking Dead
Lots of great shows mentioned here. I'll throw in The Walking Dead
Love Weeds! Since you like that you'd probably enjoy Breaking Bad too. I thought Mad Men was great and watched The Tudors on there as well. Netflix only seems worthwhile for the series though when you're looking to catch up. The selection just never seems current. Now that I'm caught up I'm thinking of canceling for a while.
Alternately, check out Hung on HBO online. Funny ****!
BBC has some great original programming:
Sherlock - a modern take on Sherlock Holmes. Only 3 episodes made so far, but the guy that plays Sherlock is perfectly cast and the guy that plays Dr. Watson will be Bilbo Baggins in the new Hobbit movies.
Jekyl - another modern day take on classic literature. This is about Dr. Jekyl dealing with his Hyde alter-ego.
Dr. Who - this is my wife's favorite show on TV. This is the best Sci-Fi show currently on TV.
The Mrs. and I just finished the original Star Trek series, which holds up surprisingly well - Netflix even has it available to watch in HD and 5.1 surround.