New Trent Easypak 7000mAh Portable Triple USB Port External Battery Charger/Power Pack for Smartphones, Tablets and more (w/built-in USB cable)
This portable battery has been great for times where I'm away from a power source and need to keep my iPhone charged.  It's about the size of a deck of cards so it's small enough to carry while it's connected to my phone and can be charging while I'm out and about.  I haven't tested it to see how many charges I get from it, but I'm guessing it's somewhere between 3-5.  I also tried charging my iPad.  It's not really designed for it, but in a pinch, it will give it all it's got, although it can't fully charg