Garmin and DeLorme have some neat little USB GPS units bundled with map software. They both cost about the same (around $100-$150) so it depends on what map software you like. They also use different gps interface standards and I think garmin uses an industry standard while delorme uses their own proprietary standard, but I could have that wrong since it's been a while since I bought one of these.
I got the delorme one several years ago and it was neat but it required 6 AAA batteries and the interface was custom and twitchy, so I quit using it. The new USB powered ones are pretty neat and some of them work with pocket PCs and palm devices.
If you have extra time, shop around, but you probably won't go wrong by just picking one and trying it out. A word of warning though, the one that bundles MS software probably works better with pocket PC devices than with palm devices.