I've been using a Fenix L2D Premium on my bike for commuting since August. I love it and will probably buy another to put on my helmet. I use the TwoFish Lockblock to secure it, but will probably get one of their new handlebar mounts as my light tends to move whenever I hit a bump. My only complaint -- and it's more of a suggestion for improvement -- is that the Fenix could use a low-battery indicator. NiMH batteries go dim pretty fast when they start losing their charge, and you can go from having good light to practically nothing in a matter of minutes. I always carry some spare AA batteries for that reason, and actually had to switch them out in the middle of my commute yesterday.

Go to the Electronics & Lighting forum here for more information about Fenix lights. There have been quite a few discussions there about them.