Petzl e+Lite or Petzl zipka. No elastic headband - instead, there's a line that reels in and out of the light. Simple to use, always the right tension, and no bulky elastic band to store. Both are light; e+Lite is ultralight, but not as bright as Zipka. Zipka uses 3 AAA batteries, and is therefore heavier but brighter.

The retracting line also lets you use either one as a handheld light or, with a bit of imagination, a hanging light.

I've used on or the other for the last 5 years with no problem.