At 15mph, getting two cateye el500's or similar lights with 1 watt luxeon LED's would work for you on a black path. The cool part would be that you look more like a vehicle with 2 bright white headlamps and if one fails, you have a backup.

Tack on an energizer recharger with 4 extra AA's that charge in 15 minutes flat and you have yourself a good package for 130 or so.

You'll get like 7-8 hrs of usable light output.

Or any 10 watt halogen would work for you. My pick would be the single halogen light and motion systems. Good mounting system and connectors, nothing that looks kludgy or home made, reliable.