GPS units preferred for bikes in order of price is Garmin 60CSX (some secondhand units out there) now superceded by Garmin 62CSX which has better image and memory and can bluetooth tracks. The best is as mentioned the Garmin montana, bigger screen better memory, it has a few minor issues that are all fixable and well documented. I used to have the 60CSX but recently upgraded to the Montana and love it.
If you have an I phone many have had good results with an app called mud maps.
Don't Tempt Fate Taunt It, Right Here Right N0W
KTM 690R 2011