Just watched the season finale of Dexter, the TV series based on the novel Darkly Dreaming Dexter by Jeff Lindsay. I've never read the books, but I must say I was pleasantly surprised and quite hooked after watching just the first episode.

The title character, one Dexter Morgan (played by Michael C. Hall of Six Feet Under renown), works for the Miami PD as an blood spatter analyst. He has an avocation, too: during his off hours, he tracks down some very, very bad people who for various reasons have eluded the proper authorities. Seems his adoptive father, a cop himself, taught the kid how to channel his dark side in a "positive" direction; and so, having captured these evildoers, Dex dispatches them with clinical precision, thus making him a serial killer who snuffs serial killers.
The first season is now available on DVD. Can't wait for the second season to start!