The WireAfter endless critical recommendation of it, and me talking about wanting to watch it, my parents bought me the first season of the Wire for christmas. It is amazing. Telling the story of one sprawling investigation that everyone wants to close down, even the heroes are wonderfully flawed- McNulty drinks far too much and is far too hot headed, Greggs (I have no idea how people's names are spelt) beats the crap out of someone for punching a police. The most interesting thing about it is that many flawed people are introduced who one presumes are just an excuse for the viewer to hate... and yet pretty much everyone is allowed more depth and complexity and that. People you expect to be idiots throughout turn out to be have far more layers than you give them credit for.
It's an unforgiving series- you need to pay attention most of the time or you will lose track of it, but it is so worth it. I will definitely be getting and watching the next 4 seasons.