The best choice?
1. Using of 1*18650 rechargeable Li battery (light, high capacity, freeze-proof)
2. Sealed metal body.
3. High power LED emitter.
Some tips:
Spark Technologies:
http://www.spark001.com/Products.aspx?ProductID=5
http://www.spark001.com/Products.aspx?ProductID=6 (360 lm!!!)
Unfortunately, Zebralight have their 18650 headlamps out of production now...
http://www.zebralight.com/Headlamp_c_7.html
but you probably find this one on e-Bay:
Zebralight H60-Q5 (info in czech language: http://www.kronium.cz/index.php?act=vie ... oductId=93)
Czech forum about LED headlamps: http://forum.fotonmag.cz/index.php?showforum=13
My tip? This one: http://www.dealextreme.com/p/flood-to-t ... 8650-44277
(very cheap, good references)