It seems like there are a lot of external batteries that you can get for your iPod/iPhone, and mophie certainly has some good ones out. This one from Kensington, the PowerLift, is unique as it is a back-up battery, dock, as well as a stand.
The 1200 mAh battery pack comes with an attached USB cord so it can be charged with anything with a USB port. As you can see in the image, the PowerLift has a kickstand that allows for putting the iPhone or iPod as a display, perfect for watching videos or using FaceTime.
If you want to use your iPhone for calls while you are charging it, no problem! All that is required is that you tack it on to the bottom of the iPhone and make your phone calls as usual. Just think of it as a longer iPhone.
Best of all, the PowerLift can fold up into a compact square that fits well in a jeans back pocket. It is good enough to add 20 hours of music, 5 hours of video, 3.5 hours of talk time, and 1.5 hours of FaceTime.
All in all, the Kensington Powerlift is a very cool product for iPhone/iPod users, and I would recommend it, especially for those who forget to charge their iDevice. You can get it on the Kensington site for about $49.99 here.