MW recommendation: "Dexter" on Showtime. I watched the first two episodes* this evening and am hooked. Bascially, the guy from "Six Feet Under" plays a forensics specialist by day, serial killer by night (but he only kills bad guys). It's kind of gruesome, but a lot of dark fun.
It makes me want to read the novel that the show is based on.
*Both of which are available as free streams at the provided link.