I'm using two conduit clamps bolted back to back. The one for the flashlight is size 0 and the one for the handlebar is size 1. They were about $2.35 for a 5 pack at Home Depot, so I have enough for 5 mounts for about $5. I put heat shrink tubing on them to prevent scratching the bike and light, but you could just as well use electrical tape or duct tape.

I learned about it here on BikeForums. Seach this forum for conduit clamps.