Giro Indicator. Your basic vented roadbike helmet.

It is a reasonably light helmet, which doesn't matter so much since I mount a bunch of stuff on it: two red blinkies, a battery pack, a (very bright) light, a (very small) videocam, and a mirror.

The dial-fit system means I can quickly go from just the helmet to adding a cycling cap underneath (rain) or a balaclava (cold).

I use this helmet for everything from commuting to century rides.