Inspire has recently released a 3 in 1 combo charging kit for your apple iphone 3g

The charger includes a USB Car Charger for on the road, a USB wall charger, and finally a USB 2.0 Sync cable. The Chargers are compatible across the board with all iPhone and iPods that use the 30 pin dock. That means it works with all except the iPod Shuffle.
You can find the Combo kit here:

http://www.inspiretech.com/p-344-iphone-3g-3-in-1-charger-kit.aspx

Here is a link to each individual product included

iPhone 3g Car Charger
http://www.inspiretech.com/p-345-iphone-3g-car-charger.aspx

USB Sync Cable
http://www.inspiretech.com/p-346-iphone-3g-dock-to-usb-sync-cable.aspx

iPhone 3g AC Adapter
http://www.inspiretech.com/p-348-iphone-3g-travel-charger.aspx