I used the
Blackburn 2'Fer as a rear helmet light. Comes with a rubber band mount that's much stouter than necessary for such a lightweight doodad. Mounts through the vents on the back of my Bell Solar road type helmet -- plenty of vents.
A "commuter" or skater type helmet would be a bit trickier. I'd use heavy duty Velcro for those. Get the kind of hook and loop tape from Velcro, 3M Command or similar stuff that's all plastic -- not fabric. I use stuff from Radio Shack that was designed to hold mobile communications devices to vehicle dashboards, so it won't budget with typical bike lights, or even my Ion Speed Pro video camera.
You can buy a pair of Blackburn 2'Fers on Amazon for $40. Good value in to-be-seen helmet lights.
Yup, reflective white bands. Continental calls theirs "Reflex" -- they're on the wire bead version of my Speed Ride tires, but not on the folding bead version. My Michelin Protek tires have them too.
Helps some but I'm planning to add some lights that are visible from the sides. On some group rides other riders have added some low power but very visible LEDs to their wheels and frames. It's impressive how much these enhance visibility without blinding other folks.
I get these in yellow and orange, a pair of the two colors for a buck at Dollartree. They hold pretty well. Just plastic, no fabric, etc., like some I've seen. But they don't cost $10-$15 like others.