A Chinese company called Fab Chain is about to add another useful function to the DS, besides its normal one as a Child Distraction Device during family car rides.
Fab Chain is rolling out a GPS navigation attachment for the DS called the Ranger. The Ranger will utilize Google Maps to display 2D and pseudo-3D maps via a U-Blox GPS receiver. The Ranger is a versatile attachment that can connect to other devices beside the DS, such as laptops and PDAs as well.
The Ranger has a rechargeable battery and can be charged through USB. It connects to the DS through the GBA slot. DSi owners are out of luck for now.
Pricing and availability will be announced shortly.