We have a Garmin 60 CSx. It's a nice unit. It has optional additional storage for maps and waypoints is rugged and accurate. It also takes double AA batteries and the run time is very good.
I know when we were shopping for a GPS about a year ago the Colorado and Oregon had some bugs. I can't remember what they were but they may have been worked out by now. As others have said, check the Geocaching forums for a wealth of information.
