I am currently using the Fenix L2D on my helmet. I used the bikeblock from fenix to attach it.
At first I had a hard time getting it aimed where I wanted it. Then I just strapped it back on the helmet and wedged a small piece of plasctic between the helmet and block to lift the beam. Worked like a charm.
I did find that, although the light is plenty bright, that cars still tended to ignore me and pull right out in front of me. I switch the light to strobe mode when I'm in traffic and now cars give me plenty of room. I've even seen traffic on the opposite side of the road slow down and pull over until they realize I'm a bike and not an ambulance or something.
I will probably pick up a second L2D Q5 version from fenix to put on the bars that I can leave on constant and on a lower setting so I can get a full 3 hours out of it for my commuting round trips. Two 2650mah batteries get about 2 hours on turbo, but a lot more on just the high setting. The high setting is plenty so see the road clearly at up to about 10-20mph depending on the lighting environment.
Another option is the Fenix P3D. It is brighter (215 lumens compared to 175) but uses CR123A batteries, which can be expensive if you don't buy online and in bulk. Local stores will charge $6+ for one of these cells and the P3D uses 2. The P3D will also drain them in about 1.5hours on turbo. There are rechargeable CR123A options, but they don't run as long on a single charge. If your commute is short or you don't need to run it at full (120 lumen mode runs almost 5 hours) power very often, this would also make a great bike light.
Be sure to get the Q5 model as it has the highest light output and has the same run times as the other non-Q5 versions of the Fenix lights.
Now get out there and ride.