I've used my Garmin Nuvi driving GPS on aircraft many times. You need to be sitting in a window, with the unit very close to the window, to pick up the satellite signals. It is tough to maintain a satellite lock since the aluminum plane blocks all satellites that you don't have line of sight to through your window. Just about any commercial GPS unit should be able to do this. Saving route information is not as common in "road" GPS units, but it is probably available in higher end units.

I've also tried using my Android (Nexus One) phone, but that failed pretty miserably. Phones use cell tower locations to get a rough lock and then zero in based on satellites. With the phone radio off, it takes forever to get a lock. I'm guessing the smaller antenna built into the phone is also a detriment to getting a lock.

Many GPS units have a jack for an external antenna, so you may be able to stick one on the window to keep a better lock. Of course you may also freak out a fellow passenger who is convinced you have just put a blob of C4 on the window and are ready to blow up the plane.

Many airlines forbid the use of GPS in flight, while many allow it - so you need to check first.