I use two (because why not?) Planet Bike Turbo Super flashes. They are white and either a watt or a half watt each...and tiny. Anyways, I run them in flash anywhere from 20 to 40 minutes a day, 5 days a week. Batteries have been lasting roughly a month before I can tell they aren't quite as bright. And by "bright" I mean "blinding". My old crackhead neighbors used to think I was the police, hehehe.

I've also used Chinese '9 LED' lights that were quite bright. I like them but the mounts keep breaking.