What is your end use? Are you wanting to use it for getting from X location in City A to Y location in City B? Mostly on-road use? Or are you wanting to use it in conjunction with topography? Are you wanting to see your location on a topo map, recording routes of off-road trails that aren't on the maps? What kind of detail do you need? Do you need something on the order of what you would see on a 1:100,000 scale map? A 1:50,000 scale map? Or do you need something as detailed as a 1:24,000 scale map? Do you want to create your own maps? Do you want to use it over aerial photography? What's your budget? Do you want an easy-to-use interface, or can you handle using software that isn't intuitive?
I know, a helluva lot of questions. But there's a plethora of different ways to skin this cat: DeLorme, Fugawi, ESRI, Trimble, Garmin, Nat. Geo., Magellan, etc. etc., lots of different choices, depending on your needs. Lemme know what your goals/desires/limitations are, and I'll try to help.......
-L