Nothing will tap an iPhone battery faster than a day at Macworld Expo. The constant barrage of data traffic in the form of texts, email, Web, GPS, Bluetooth and WiFi will drain the battery before you make it to Dim Sum for lunch.
An external battery pack is easily one of the most practical accessories for the traveling iPhone and my favorite is the iV from FastMac ($79). The iV is a sled-type battery pack that packs 3100 mAh – the highest capacity in its category. By comparison Richard Solo and Mophie's Juice Pack top out at 1800 mAh, while the InCase Power Slider is 1330 mAh.
In addition to being able to fully charge an iPhone more than twice, the iV doesn't obscure the camera and has pass-throughs for the speaker and microphone. It's also dockable in the Apple dock and comes with a super-bright LED flashlight for finding your keys or for taking pictures in low light. The icing on the cake is the extra USB port that allows you to easily charge a Bluetooth headset without tying up another port on my MacBook.
Extremely well done and a O'Grady Best in Show award for 2009.