Like its name implies, the Juice Pack Reserve by Mophie ($35) has the power you need to charge or extend the battery life of your iPhone or iPod.  This lightweight and compact charger comes with a convenient key ring so you can recharge your device whenever you need it. It features high-output battery to quickly transfer power, a built-in USB charging cable and 30-pin connector and an integrated LED power indicator to keep track of power status.