I'll second/third/whatever :

Community
Mad Men
The Wire
Cowboy Bebop
Buffy seasons 1-3
How I Met Your Mother seasons 1-4
Battlestar Galactica

 

I don't doubt it. It's just that I've only caught a few episodes over the years and didn't really have much of a basis on which to recommend it. (It came out when I was in grad school and didn't even own a TV).

 

Shows I'm currently following:

Star Wars: The Clone Wars (Season 3 is halfway done, next episode is on Jan. 10)
Family Guy (It's a Twap!)
Bones
Dexter
Criminal Minds
Phineas and Ferb

 

Jekyll - a BBC mini-series from 2007. James Nesbitt is all kinds of awesome in this. You will fap to the first transformation scene.

 

Scrubs is one of my all time favorites.

 

Weeds

And I'll second whoever said X-Files. Seasons one through three were some of the best, IMO. After that, things started going downhill.

 

Lost
Boardwalk Empire (HBO)
House
Avengers (Earth's mightiest Heroes)
Fawlty Towers (BBC reruns)

 

The Wire/Sopranos/Deadwood combo
The Boondocks
Man vs. Food
Scrubs

 

Lie to me (Can't believe no one recommend this one so far)
NCIS-LA
Undercovers
Hellcats

 

Totally forgot about Breaking Bad, as the third season isn't coming around for a while. What Coyote said is truth, totally amazing show.

 

Because after the first season is sucked major balls?

 

South Park. Heroes season 1 also I guess. Only season 1 though.

 

Everyone should watch at least the first season of 24.
The West Wing
Californication
Weeds
Scrubs

All really worth watching.

Edit: Also for something completely different, old British comedy shows are good. Blackadder (season 4 is genius), Fawlty Towers is pretty good; for sketches Monty Python's Flying Circus, A Bit of Fry and Laurie.

 

The OP is the one who said Firefly...in the OP.

On topic: Dexter is pretty fucking awesome. So is Breaking Bad.

 

Another shout for Breaking Bad.
And once you've watched that, move onto Mad Men.

 

Seconding Castle. I don't watch much TV so most of the things in this thread are new to me.

 

Trying Raising Hope. It had an interesting opening, but so far its potential for dark humor has only been sporadically realized. It's an okay show if you just wana blow off some stream, though.

 

Todd and the Book of Pure Evil is soon coming out on DVD, and you can watch it all on Space.com. It's my favourite TV show of all time, if onyl for its cool premise and characters.

 

Well, Top Gear is on your list, so that throws about 75% of my TV material out. There is several different versions though. UK is the major one, and the new season starts this month. Must watch, even if you don't like cars. US version is decent enough for being brand new. TG OZ is good too.

Stuff that hasn't been said yet that I enjoyed.
Brainiac Science Abuse
James May's Toy Stories
James May's Man Lab
Oz an James Big Wine Adventure
(See a pattern?)

Carl Sagan's Cosmos

Then you get to a lot of the History and Discovery channel staples.
Survivorman (10X better than man vs wild)
Deadliest Catch
How it's Made
Future Weapons
Dirtiest Jobs
Mythbusters
The Colony
Iceroad Truckers
Then there are a ton of lumber harvesting shows (axemen, swamploggers) and a bunch of pawning/auction shows (pickers, pawnstars, hardcore pawn). I like them, but it is a hit or miss.

-edit-
a few more I forgot about
the Adam Corolla project
Monster Garage
Monster House
High Stakes Poker