I've found that lowering the light too much below the handlebars casts odd shadows. Mounting it on the fork tip like the Problem Solver does makes shadows very long and distorted. Mounting the light at the handlebar level is just about optimal.

Some of the other ideas mount the lights in places where you could catch them or hit them in a crash. You don't need to increase the level of possible injury if you crash. The best light mount that I've found that doesn't take up any handlebar space and puts the light in a good position is the Dijia Cycleworks mount from Velo Orange. It takes the place of 2 of the mounting bolts on the handlebar front face clamp. The only caveat is that you have to have a 4 bolt face plate.