The iPhone 3G Juice Pack ($99.95) from Mophie extends your iPhone's battery life, making it a must have for many iPhone owners. Starting with a fully charged iPhone battery, I was able to squeeze almost 24 hours of normal use out of the Juice Pack before the iPhone's internal battery took over.

The Juice Pack is powered by a rechargeable lithium polymer battery and incorporates four LEDs to indicate the remaining juice. You can easily slide an iPhone into the black-and-green Juice Pack, which powers your device through its dock connector. The device doubles the phone's thickness and adds 3 ounces to its weight--a small price to pay for a full day of phone calls.

A mini-USB port (and included cable) lets you charge the device simply by plugging it into your computer and enables synchronization if you leave the iPhone in the device while charging.

The Mophie Juice Pack is available for the iPhone and iPhone 3G for $99.95 from the company's Web site.