Scosche reVIVE II Dual USB Car / Charger Adapter for Apple iPhone 4, iPhone 3G/3GS, iPod touch, nano for $11.99 + free shipping
Use your existing USB cable to charge 2 devices simultaneously! Simply connect the USB cable (not included) to your phone and then to the charger module. Now you still have an extra USB port to charge another device! It is convenient and easy, now you don't have to bring extra charger anymore.