I recommend the Garmin StreetPilot III or StreetPilot 2610.
I have the III and it is amazing. It really works and knows even the smallest roads and new developments. Put in an address and it will lead you to within 20 feet of the front door. It tells you every intersecting road as you come to them, and also shows you the street address your at on the road your presently on. It gives you voice prompts like "In 300 feet turn left, then turn sharp right. Drive 7 miles"
My only complaint with the III is that it uses a proprietary memory stick that is 128MB MAX. It comes with a CD containing all of the USA and Canada, but you can load only a small portion into the memory stick. For me that’s most of the state of PA, and some of NY, NJ, MD.
In addition to the detailed maps in the memory stick, both units contain a base map of major highways and interstates for the entire USA. This means that you only have to load detailed maps for your destination, not for the entire route.
The 2610 has a touch screen, which I’m not wild about (I'd rather press buttons I can feel), but it has the advantage of taking standard Compact Flash memory. Not only is that cheap, but it is available up to 2GB, and maybe 4GB by now. (the compact flash standard allows a maximum of 6GB). I think a 1Gig chip would be great and not that expensive.
I recommended one to another list member who bought the 2610. If you're there, tell us how you like it.
Best regards,
MikeC