The CygoLite NiteRover costs about $70-80, puts out a lot of light and holds a charge for a long time. It has two lights, low beam and high, which you can run separately or together. I've had one for about 5 years with no problems. On low beam (which is enough light for commuting on my route), it holds enough charge to last me 4+ hours -- which amounts to a whole week of commuting for me. I only use my lights in the morning, and my commute is about 45 minutes each way.

Some of the LED lights might also be good options, but I personally haven't tried them. The various Fenix flashlights seem to get good reviews, and they sell and optional mount for handlebars or helmet. They have long run times but I don't know how their brightness compares with a halogen light such as the Cygo.