The most efficient headlights will use LEDs, but they are expensive unless you build one yourself. With that being said, dynohub lights are sooo much nicer than charging/replacing batteries all the time. Probably the best, cheapest solution would be to get a very nice Cree LED mini flashlight from Dealextreme.com and mount it on the handlebars... and if 1 isn't enough, they're cheap enough to get two.

A flashlight like this:
http://www.dealextreme.com/p/uniquef...500-1-aa-55243

and a mount like this:
http://www.dealextreme.com/p/univers...m-32-8mm-15342