Android : OffLine Map App
If, like me, you use your 'Droid only in wifi mode then you may regret not
to be able to use google maps whenever you get lost, outside civilization, far
from a wifi access-point.
Then the MapDroyd app was made for you.
After an initial/install-time download of the "Open Street Map" project's maps relevant for you, you are ready to go
For the moment, it is not on the market but available at http://www.mapdroyd.com/