Mountain Bike Lights.
Wolf-Like Cujet said, there are many, many bicycle lights available for varying prices. Some have dual-beam headlights and some also include helmet-mounted lights. Most have the battery packs inside a water bottle-shaped holder for mounting in a water bottle cage on the bike. If you have a fanny pack that carries water bottles, you could carry it there. You could even carry a spare batt in case you're out too long and run the primary down.
Not sure which of these companies have websites (they all probably do) but here are the three mail-order catalogs that I receive:
Colorado Cyclist
Performance
Bike Nashbar
Do a search and you should be able to get some objective ideas about which system would suit you best, run time, wattage, etc.