The Wire is excellent if you prefer you're cop/crime drama with depth and real social awareness rather than the normal stereotypical cop show sh!te. Omar White is the greatest character I've ever seen on TV. All 5 seasons are top notch but season 4 is the one that really hits home.
I gave it a 10/10 on IMDB.
It is better than the Sopranos , which although still excellent didn't seem to have the same grey area personalities. I always found Tony just a bit to one dimensional for instance. I still gave it a 9 on IMDB tho'
Deadwood is another brilliant HBO show. anything where Lovejoy says fcuk and cnut 50 times and episode has got to be tho' hasn't it?
Oz starts of a bit cheesy and stereotypical but does get better and better.
Just started watching Treme which is by the same bloke who did The Wire. It's a bit of a slow burner but I'm just getting into it on episode 3 now they've introduced the characters.
Basically HBO tend to get it right.