EXOGEAR iPhone 4 battery case
image from exogear.com
This is a great-looking external battery case from EXOGEAR. I'm actually surprised that Mophie hasn't come out with a case like this (they offer new external battery packs for the iPhone 4 that attach to the dock port), since they've had success with the Mophie juice pack air. Anyway, I'm probably going to buy this battery case because while I get pretty good battery life in normal, day-to-day use, when I use the iPhone as a camera for an extended amount of time, the battery is depleted more quickly. Since the iPhone 4's camera is so good now, I definitely use it more.
I like that the case seems to be clear on the sides so that it still shows off the stainless steel band around the edge. I like this industrial design and have been wanting a clear case that keeps the band visible.