The Wire is great, and I keep meaning to watch The Shield, but I have a hard time pushing myself to watch something that I know is going to be dark and depressing. I've also heard great things about AMC's The Killing, so I may watch that once the season concludes.
I can't stand all of the crime procedurals on CBS, though. It's like there are 5+ versions of the same show, where the characters are dull and underdeveloped and the killer is always caught at the end of the hour. I much prefer shows like The Wire, where you can't go into every episode knowing exactly what to expect.
I've thought of maybe possibly check out Bones because it seems to have quirky characters, but I've been reluctant to do so. But at least it's not on CBS, so it's got that going for it, I guess.