I use a Fenix LD20 on my helmet, but it's really more of a backup or secondary light. It's actually bright enough to use by itself, but may not provide enough lumens for some. The nice thing about helmet lights is that you can look at drivers pulling out from side streets, parking lots, etc., and freeze them in their tracks. However, they are not as effective at lighting up the road ahead, IMHO.

I just ordered a Light & Motion Stella 300, which can be mounted on helmet or handlebar. That would be a good option to consider because they are high quality, relatively light weight, provide good mounting options and recharge relatively quick. If you shop around, you can find excellent prices.