I have an eTrex Legend ($150 at Circuit City) I use in the car. It's good for finding the nearest highway.
The benefit of paying a little more for the Legend, is that it includes a serial cable.
I like to create directions in Google Earth, save the file, convert it with gpsvisualizer.com and load it in with EasyGPS as a track. Using the track, the compass arrow indicates my exits and turns, even if the road isn't on the base map. It's a bit complicated, but cheaper than buying the maps.
I subscribed to the premium Google Earth, so I can directly load my track logs and review where I've been.
I miss having a color screen. It'd be a lot easier to see a track in color while driving.