Finally, something I'm an expert in!
We used to buy a couple of these every trip we went on to test them out. My favourites and not favourites:
Petzl Tikka Plus 2 $70
Good light, water resistant, OK with batteries, lightweight, good strap. Perfect all-rounder.
Energizer headlight $34
Best value light out there. It's the one in your grocery store battery section. Cheap, seems to work on one set of batteries longer than any other, red LED for night vision retention. Strap is OK. Not sure about water resistance, but this is probably my favourite light.
LED Lenser H7 $80
Bright! But LED adjustment doesn't work that well. Batteries on the back of the head makes sense, but feels weird. Heavy, no battery life and mine broke pretty quickly. The wiring inside is very brittle.
Black Diamond Spot $70
Water resistant, lightweight, everything the Energizer one is except a bit smaller and more expensive.
Seriously, a few grams makes a difference when it is perched on your forehead for hours at night...but then, so do a few dollars when there aren't many around...
that's my 2 cents.
Carlisle