If you’re interested in developing applications which make use of GPS hardware, be sure to check out Sparkfun. They sell all sorts of parts, including tiny GPS receivers, cellular and Bluetooth communications modules, development boards, LCDs, and tons more. What suprised me is how affordable most everything is! Usually hardware in that area is expensive and complicated.
On a related note, a clever hacker adapted a GPS module to communicate serially with a Nintendo DS, and integrated it with Google Maps, so you can now view maps on the DS. The Nintendo DS wi-fi protocol has not been reverse enginnered yet, so the maps must be loaded prior to execution, however I’m sure it will all come together in time.