I got one of these on eBay for much less than MSRP -

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

Basically what it is is mapping software that gets you from point A to point B along navigable paths with the benefit of turn-by-turn directions (turn left here, turn right there). The GPS receiver tells the software where you are at a given moment so the software can determine where to put an arrow on the map, in what direction you're going an how fast.

It works well except that even on full blast I can't hear the PDA over the stereo at moderate levels, and preventing the screen from dimming uses up battery charge very quickly.

Sixto
93 300SD