I spend lots of time on the road and I have a few devices that can be charged with USB. My ipod Touch, my Android phone and my digital camera, these devices can be charged via a usb port. Since my office is my backpack, anything to shed weight is good.
My "main" charger is from iGo. It's called the iGo Anywhere. What makes it better than a regular USB wall wart type charger is that it has a battery inside the body of the charger. What that means is you can charge as many as 2 devices at once even if you don't have access to a wall outlet. There are many days where my Droid Eris phone will die in the middle of the day and I won't have time to plug it into an outlet. I pull this little baby out of my bag, plug in the USB cable and in about an 45 minutes, it will restore my phone to about 75% battery.