I have one of these:
http://www.amazon.com/gp/product/B001TQ6DI2/ref=oss_product
It's ungodly bright (seriously: brighter than most motorcycle headlights), mounts nicely on my handlebars, and works on 9 to 60 volts. I have a dc-dc converter on my bike anyway, because I have a Stirling fridge...