I have a Garmin iQue 3600 and love it. Since I don't geocache as much as I drive in the car I got a GPS more tuned to street navigation. It also works good for geocaching with a few free add-ons. Most GPS only devices are not as hackable or expandable as a PDA/GPS or pocket PC/GPS solutions.

If you have a PDA already maybe something like this will do the job….

http://www.garmin.com/products/gps10/

http://www.garmin.com/products/cfQue/