I recently came across these Reelights , They work by fixing two magnets to the spokes. When the wheel spins, the magnetic field causes a current to run in copper wires inside the lamp housing. Power is stored in a capacitor, so the LED lights will stay lit when you stop, and the output is steady, regardless of your speed. So you don't need batteries, and you won't forget to bring it because it's stuck to your bike. I hope I'm not behind the times on this one, but I thought it was smart.