Excellent thread! I was just looking up information on installing LED bulbs on a headlight to maximize battery use.
I also came across these LED bulbs designed for autos. Maybe if you tinker around with a couple of them and align them just right, you might get some decent lighting. Well, maybe at least for driving in areas were its not pitched black.
They are pretty cheap, I think they might be worth a shot:
2 X H3 Headlight Fog Light 9 SMD LED Xenon White Bulbs - eBay (item 130352670433 end time Jan-14-10 15:49:07 PST)
H11 36-LED Car Fog Headlight Light Foglight Bulb Lamp :eBay Motors (item 160373677145 end time Jan-27-10 01:54:48 PST)