Luther is very good. It seems over stylised at first, but you stop noticing that and get drawn in. I like the way it cuts out a lot of the cop-drama staples, most of what you'd see in a morse/frost type detective drama is despensed with in a few minutes, the rest of each story sits in a place after the credits would have rolled in a normal show.
The Wire is superb but you need to have the time to give to it, and you'll squander it if you don't. Its very good in its own right but its also good in a way that renders a lot of other tv drama redundant.
Old episodes of taggart are good for a laugh, just because they are so slipshod, some of the laziest TV making making you'll ever witness. Why shoot a scene in multiple takes and multiple angles when you can just cram everyone into one shot, usually talking to the side or back of each others heads. Sometimes they cram the cast so close together the look like they're going to kiss. That and clangers like car chases where both the chaser and the chasee are driving the same make, model and colour of vehicle make it strangely compulsive viewing.