Dennis -
You are correct about the GPS screens being small, but you should look at the GPS unit as being part of the solution along with the laptop. I would recommend looking into a GPS that has the ability to be used by itself, or used with a laptop and your choice of software. Most any GPS offered by Garmin, Magellan, or others will work as I described using industry standard communications and a serial or USB port.
The benefit is that you have more capabilities with a fully functional GPS compared to a GPS sensor only. For example, you may want to carry your GPS with you and have it track and remember a drive, hike, hunting trip, motorcycle ride, etc. and then upload that data to your laptop and application to get trip statistics, topographical maps, saved points of interest, etc. With a bundled software/GPS sensor solution, you would not be able to do this unless you carry your laptop with you everywhere you go. And as far as mapping and route calculation, many of the small GPS have those functions now, and you can always hook up to the laptop and let your powerful software do the job when you are on an appropriate trip.
Personally, I use a Garmin Etrex Vista GPS and for software I have MS Mappoint, TOPO!, and Mapsource. The GPS goes with me into the outdoors, and the data is then later loaded to the laptop for different things. I can do it the opposite way also, I can create a trip on the laptop with any of the apps, then move that route and waypoints to the GPS and let it guide me. This works on the streets or with topo maps for the wilderness. The Vista also has an electronic compass, altimeter, trip computer, fish/hunt calendar, and many more functions, and retails for about $300. A small price for the features, but like you said, not a screen that you would want to drive by for a whole trip. That's where the laptop comes in.
I mention this just to be sure that those of you new to GPS have an idea of the functionality of the smaller units. This setup works well for me, and may for many of you if you want the same capabilities.