Most Stylish: Mophie Juice Pack Plus iPhone 4 & 4S Battery Case ($99.95)
If you find yourself constantly running low on battery during a workout or at the bar, then look no further than the Mophie Juice Pack case. This sleek case comes in seven different colors and offers extended battery life for up to eight hours through an attachable battery pack built into the case. The case offers standby and charging modes, which let you choose exactly when to resort to the backup battery.
Four LED lights on the bottom of the lightweight case tell you how much juice you have left and let you know when the pack is fully charged (make sure all four light up to confirm that your phone is fully charged). The hardshell case and rubberized band provide additional safety without adding bulk.
Available at Mophie.com.