+2 for the garmin Montana. The largest screen, waterproof GPS available that does offroad really well. It also takes the punishment of hare scarmbles and enduro races.
I have looked at lots of GPS apps for android and some of them are just OK for offroad use, but none stand out as really good. You need offline maps, import/export of GPX files, tracking, waypoints, camera is nice too. I have a galaxy tab and I can get a waterproof case, problem is getting power to the unit is a pain. I am sure I can make it work, but its just plain easier to stick the with Montana.