I'll second the ability to interface with a computer.

A basic GPS really doesn't have to have many features, nor does it have to have a large display, but one thing I myself hate is entering waypoint coordinates and routes manually via the GPS keyboard. It is much MUCH easier to enter them via a computer. I use both ExpertGPS (expertgps.com) to identify waypoints and routes on on-line maps and then transfer them to my GPS.