Before I begin, I'd have to say, the lack of color certainly makes it interesting. Without it, no sig can jump out on it's own. I mean, before, if someone posted a very colorful sig, it'd immediately stand out to you. This week, though, no sig suddenly caught my eye. It's nice, to say the least (not saying that colorful sigs are annoying, they can just be distracting at times).
Anyways, while they're all good sigs (yes, Beeslo, even your's =p), I'd have to go with Crittbeast for this one. Like Link and Snake said, it looks great in black and white, which is odd, because you'd have expect it to be, well, not that great without color. The addition of Brock was also pretty funny, and props to him for adding that. The greyest white look for their skin just contrasts well with the darkest grey look of their clothes. You especially notice this with the girl in the middle (Dawn?), thanks to how much skin is showing and the color of her shirt. While the contest was intended for images that were originally black and white, Crittbeast still did an excellent job, because he picked the right contrast for the sig.
Yeah. I played with the contrast options in photoshop A LOT before I was happy with it.