Nobody mentioned the Magnic Light. I don't have one, nor have I ever seen one, nor do I have anything to do with them. But this seems like a great solution because nothing more than the light head is needed. It relies on the eddy current from the spinning rim and makes no contact.

I may just order a tail light as a starter. I also like the brake light function. Basically when you apply the brakes the light head, which is attached at the brake pad holder, gets closer to the rim and generates more current. They are a little pricey, but I'm willing to give it a try.

Edit: I ordered the tail light. The full set gets even more pricey, but I'll see if I like it on the rear first.