I have made several bike mounts similar to the one posted by Athens80 using PVC pipe fittings from the local Ace Hardware. The cost is less than $2 each. All you need is a short connector and plug. Then I drill a hose in the middle of the plug, just large enough to run a bolt and washer through it. Finally, I bolt the PVC mount to my bike frame. I usually put the PVC mount on one of the rear chainstay rack mounts to hold my Dinotte taillight while commuting. However, I also have used it on the front fork of my touring bike to hold a headlight.
Regarding headlights, I highly recommend the Light & Motion Urban series for a front light mounted to a fork. Not only are they very bright with excellent run times, they are also very compact and light weight. My Urban 800 weighs only about 120 grams.
In the attached photo, you can see the mount on my bike's front fork.