Cygolite Expilion 250 mounted on my helmet.

This little light is extremely bright, weighs very little, and has just the right beamwidth and throw to compliment my handlebar mounted light. Having a light on my helmet makes a huge difference . . . I can see much better going around corners and throw a little light (or a lot if necessary) onto a driver's face to get their attention. The adjustable helmet mount allows me to aim the light down so as not to blind oncoming riders, and then aim up higher when there is no oncoming traffic. It has transformed my night riding.