Have you guys seen this Airbike P7 light on ebay? It looks very good for the price, its about double what a P7 flashlight and mounts/batteries would cost but the fact that it's designed for easy mounting and has an included battery pack and charger makes it pretty attractive. I found some discussion on it MTBR but nothing definitive (edit: found one review (pretty positive, with pictures)) . In terms of lumens/$$ it isn't too far some of the DIY options or flashlight options I see but is more refined than both of those options (unless you have some seriously good DIY skills. To me, 670 lumens for 3 hours is pretty solid.
Check it out and share your thoughts.