Mammut X-Zoom
An excellent headlamp. 3 levels of brightness, with a zoom feature that spreads the light from a wide field of view all the way to a very tight rectangle. At the highest power and highest zoom it is very very bright.
I have used it for skijoring and scootering and other activities with my dogs. One of the features I like is that it has several red LEDs on the back that you can turn on as flashers that help keep you safe on the road.
The light uses 3 AA batteries. It's pretty comfortable on my head and easy to adjust the angle of the light up and down. I've owned three headlamps, including a 15 year old Petzl with a big battery that I used for mountaineering. This one is much more practical in terms of size, comfort, lighting options, easy to get batteries, battery life, etc.
Not sure how long it will last on one set of batteries but I've used it a fair amount without any dimming so far. It is an LED so I expect it to be very energy efficient.
Update: November 17, 2010
Update: I've had this headlamp for nearly two years. I've used it almost every night since I bought it and still like it a lot. AND ... I've yet to change the batteries. It's dim now and they need changing but that is a phenomenal life span.
This one needs to go back to Research and Development. Unless you use lithium batteries it's WAY too heavy. Even with lithium batteries, the light digs into your forehead making it uncomfortable to wear for more than a few minutes. If you wear a stocking cap or helmet all the time it might work for you but I wasted $100.