I use a
Cateye HL-EL530. I wish I could say I recommend it but alas, I cannot. It's okay, just underwhelming. I do like the fact that it's self-contained and runs on 4 AA batteries. I also like that it only has one steady "on" setting (I have a backup blinkie). It does help me to define potholes, but it's output is less than impressive.
I mounted it to my fork crown using an
Ixon Speed fork crown mount (scroll down the linked page to see it) that I got from Peter White Cycles. He offers a lot of different battery-powered lights that are a step above the 530. In fact, he has this to say about the 530:
The newer EL530 is brighter but still a small beam. Not enough to light up the road by itself. If this is your only light for use on unlit roads, you'll want two of them, perhaps three.
I guess I should have done my homework a little better. If I were to buy another battery-powered headlight it would be the
Busch & Müller Ixon IQ Speed.