I use an older Light and Motion ARC HID light on my helmet. Low setting is 550 lumens, high setting 675 lumens. I run it low most of the time, and there’s not much difference visually between the two settings. Light and Motion makes good quality lights, but they’re a bit more expensive. The light is pretty “floody”, with a bright spot.
@CyclingGirl runs a Light and Motion Stella 500 (500 lumen) LED on her helmet. My perception is that it has a more uniform beam pattern, and is a tighter beam.
Light and Motion no longer make the ARC or the Stella. Their current equivalent is the Imjin, which is an 800-lumen light.
I also have a 500-lumen Planet Bike LED light that I run on my bar as a spare in case the battery on my helmet light runs out. It’s plenty bright, and tighter beam than my L&M ARC. The light pattern is not as uniform as the L&M. Some darker and brighter spots in the beam. It was about $60 when I bought it. The updated version from MEC is 650 lumens and listed for $75:
The LED lights with the integrated battery seem to be popular. All of the local bike shops will have an equivalent.