We've seen portable battery packs before, but XPower's Xantrex Mobile Mini charges two things at once. Two. That's double the amount of things charged as one. Just FYI.
The Mobile Mini has a USB port so you can plug in just about any USB-friendly charger, like the iPod or the Zune, and has a miniUSB port so you can juice up your Windows Mobile phones as well. At $49, it's not too expensive, especially since it charges...what was it again...oh yes, two things at once.
Product Page [Prepared With Power]