I have a DeLorme PN20 GPS. The best thing about DeLorme's GPS units is they come with DeLorme's Topo USA mapping software which is excellent. I use the PC mapping software to map out a ride, then I can check the elevation profile, and finally download it to my GPS along with appropriate waypoints -- bakeries are my favorite waypoint on tour
The PN40 uses the same maps but has a MUCH faster processor. If you download a lot of map layers (you can load road layers, trail layers, satellite imagery, aerial imagery, topo countours) the PN20 will take a few seconds to redraw; I understand the PN40 is really snappy, but more $.
REI carries the DeLorme GPS units (along with several others).