Third Rail Mobility, a case/battery system that our own Mike Rose reviewed (and liked), announced revisions to their iPhone 4/4S case and battery systems at CES 2012. Now they are available in colors aside from black, allowing you to customize your iPhone and keep it charged. Soon their line will include green, red, pink, white, purple, and blue.
On the off chance you want to keep your black case but add an extra layer of protection or just accessorize a bit based on whatever outfit you're wearing today, you're also in luck: Third Rail has also announced a line of silicone "bumpers" that slip around your existing Third Rail case in assorted colors, letting you choose a color and yet still use your battery. And while they were at it, Third Rail Mobility also announced a new battery for their cases, a 2000 mAh capacity battery which will more than double the life of your iPhone 4 (1420 mAh) or iPhone 4S (1432 mAh).
Their cases are a twist on the battery case style we're all used to seeing: the battery snaps into the back of the case, so when you don't need a battery you have a nice trim case, but when you do need one, you just pop it on the back and you're ready to go. Another nice feature: You can attach multiple batteries together, so when one runs out, stack another one on top and keep going. Third Rail cases also have a power switch, so if you want to charge up at strategic intervals you have that option as well.
These updated versions of the Third Rail Case will be available in the spring.