The Wire>>Breaking Bad (and everything else)
But, Justified is I think the most fun 'gritty' show on right now. I could wax philosophical about how much I love that show for hours.
If you like watching people curse like sailors and beat the crap out of each other (as does every red-blooded American), and you enjoy complex morally ambiguous characters, HBO's Deadwood is a personal favorite for me.
HBO's Rome is pretty awesome also, especially in the first season.
My friends love Spartacus, personally I think its over-done and stupid.
Ummm...
Community is funnier than anything out there, and its about to come 'back on' in Feb, all 3 seasons are available on Hulu.