I usually have a map and compass for backup. It was very nice having the gps when we did a longer than usual ride and spent the last 3 hours of our ride in the dark. I just kept the gps zoomed in so I knew if I had gone by a turn we needed to take. Had to backtrack a couple times. Everything looks different in the dark.

 

Garmin Montana has a nice big screen, rechargable battery and is street or topo compatible. They had some bugs in the software early on but are good now. Available in with or without camera too. The camera will tag you picture with a gps location and can transfer data wirelessly to other garmin wireless units.
The montana is a bit big for hand use, but is perfect for off road or on road vehicles

Ram mount is the best way to go, holds my gps, hand held vhf radio or I phone.
Ken