I prefer the SB L-Mini for a helmet light, one of the smaller 18650 lights on the market and now uses an R2 emitter.. I know it's only 250 lumens but the runtime is solid and the light is very small and you hardly even feel it on the helmet..
For mounting you can use the Bikeblocks, parallel mounting, same company that sells the Lockblocks for the handlebars.. Or the Zefal Doodad works great too..
http://www.amazon.com/Zefal-Doodad-P.../dp/B000AO3FTE
http://www.shiningbeam.com/servlet/t...iniI-II/Detail