I got this off of WMpowerusers which is running quite slow nowadays.
In the days of expensive GPS systems like Tom-tom and Garmin, and Google Navigation that is limited to Android, a new service brings you free maps. The new application is called OpenMobileMaps and it was just released today. The application allows you to download all the maps you need for your phone and then use it to get around town. The application does allow you to store not only in your phones memory, but your SD card. The app is 100% free and is something to think about till Google Nav is available for us.
original source:
http://forum.xda-developers.com/showthread.php?t=597957