IQUE 3600
I use a Garmin IQue 3600 for my navigation. It is a pretty good package. I have the "bean bag" mount which is fully adjustable so that you can see it in almost any light conditions. The screen is larger than any other, non-permanent GPS that I could find. The antenna is a flip-out on the back of the unit and opening it automatically puts you in GPS mode. The power adapter with the mount has a built-in speaker which is plenty good enough. It is super accurate. I have never found a problem with getting from Point A to Point B in a reasonable fashion. The maps were just updated (2004). The cost of updating was around $60 us. As it has a cradle for the computer, the mapping software also works on your PC. Therefore, you can do all of your planning on the 'puter and then just load it up to the GPS and you're off. It helps to use the larger screen. There is a couple of drawbacks. The first is the battery life when in GPS mode and not in the vehicle is very limited. I'm guessing a couple of hours at best. The other drawback is that Garmin uses a field effect transistor to know when the GPS antenna is extended. On some vehicles (mainly older than 2002), when the vehicle is started with the unit plugged in, it will fry this transistor. Garmin has said that this is not a problem on later vehicles as the filtering on the power supply is good enough. I've used it in several vehicles 2002 and newer and never had a problem. My friend, however, has a 1999 Durango and he has.
All-in-all it's a good unit for the money if you want a good unit, Palm OS, and portability. Note that there are also some add-ins now for the pocket PC's as well. Good Luck with your search.
ShraderMan