There were two things that almost prevented me from getting an iPhone, the reportedly poor battery life and the fact that I had invested a lot in Blackberry chargers/cables, etc and didn't like the idea of moving to a new standard.
I found a solution to both of these problems in an unexpected place. After purchasing my iPhone, I started researching both external power supplies and protective cases for it. The JuicePack and the Power Slider address both problems simultaneously, but I decided that they were both too bulky, especially since I only needed to use the external battery on occasion and would have ended up carrying it around everywhere. I eventually found the APC Universal Battery, 10WH which foot the bill as an external battery pack. It seemed to be the best reviewed out there, so I took the plunge.
What I did not realize was that I was also getting a iPhone adapter for my old blackberry chargers. You see, the 10WH (crappy name--those guys at APC need better marketing) is charged via a standard USB charger, the same that is on the Blackberry. Furthermore, the power output to the iPhone is via a USB port. The device supports a passthrough charge. In other words, you can plug the 10WH into the wall and charge the external battery and at the same time have the iPhone plugged into the 10WH and get it charged as well. Voila! Two devices charging on one outlet, and I found a use for my old blackberry charger! At $65, it is more expensive than buying a $21 Apple charger, but it has the external battery and the ability to charge many more devices (any usb device). To me, it was well worth it--I just got two devices in one--an external battery and a wall charger. Awesome!
Incidentally, this is the case I ended up purchasing.