These may be more common in the world of bikes that I realized, but I like the way the "Reelight" LED bike light works. Instead of using a dynamo to generate electricity like bike lights of the last several decades, the Reelight uses two neodymium magnets to charge a capacitor. Gadget Lab even supposes that more magnets could be clipped onto your wheel to generate extra power, which could in turn be used to top off phones and the like.
From what I can tell from reading the Amazon reviews, however, these only blink when the magnets pass, meaning it's unlikely they'd generate all that much power in the first place. It looks like you'll have to stick with the dynamos to power real headlights for now.
The Reelight is $40 for a set.
Product Page [Reelight.com]