Hello

770/800 screen is good for navigating and battery life time is guite good.

S60 and Pocket pc there is good software but both devices has poor displays.
hXXp://XXX.wild-mobile.com/ SmartcomGPS for S60
HXXp://XXX.oziexplorer.com/ Oziexplorer CE for Pocket PC devices

Now Nokia 770/N800 needs something like that

Good feature these two software is you can use large resolution images.
Example one 8000X5000 image.