To use the Sony PSP as GPS navigation device is one of the most thought after non-gaming features of the portable console.

Sony has announced a GPS accessory for the PSP back in March dubbed PSP-290 that is supposed to come in October on the market.
Sony already released map viewer software for the PSP in Japan. Play-Asia sells 'Minna no Map' for $42.90. It only has maps for Japan, so not useful for the rest of the world.
Until Sony is going to offer the GPS accessory and/or global map software we have to rely on the Sony PSP homebrew community.
The first hack dates back already to 2005, where the homebrew program called GPSP was able to read data from a GPS mouse.

The most advanced homebrew GPS and map viewer software today is the Deniska Map This PSP Map viewer. Here is a pretty impressive video demoing the PSP navigation hack driving around in a car. In this post Deniska explains how to hook up a Holux GPSlim236 GPS receiver to a Sony PSP. Deniska's latest public release GPS/Map viewer software is available here.

We collected Sony PSP feature requests way back in 2005, which already included the GPS feature request from I4U readers.