I use OruxMaps on my Acer A100.

I attached mine to my Vector e-dock using a RAM mount. I placed it in front of the radio because I also use it for music playing and other apps.
The A100 runs Honeycomb but you may want to check the Apple store to see if they also have for iOS.
OruxMaps can download Google Topo Maps for off-network use. Works great.
Only thing is that the maps can take a lot of memory space if you download the full resolution. The A100 allows for storing stuff on external memory cards, so not an issue for me.