This gadget attaches to your wheel spokes with zip ties. The set of bright, colorfully flashing LEDs makes cool persistence of vision patterns as you roll. These even work well in shade (like we have in the Santa Cruz Mountains) and overcast skies (like we often have in San Francisco).
These guys do a fantastic job lighting up the ground around you.
These are about twice of the price of comparable Hokey Spokes. Monkey Electric lights do not sync up like Hokey Spokes do, but then you don't need two or three units to make a decent pattern, and the LEDs on the Monkey Electric lights are much brighter and colorful. Some people like the aesthetics of Hokey Spokes better, and I think Monkey Electric are a little bit less resistant to theft since all you need to do is snip three zip ties to take these things; Hokey Spokes are secured with screws.
For details and online purchase, visit Monkey Electric. Use the coupon code "BIKECULT" for 25% off of your order until July 15, 2008. Order fulfillment is quick, shipping is fast, and installation is no problem at all.