I have the Garmin GPSMAP 60CS and I love the thing. I did quite a bit of online research before buying one and decided on this one because of its weather proofing, sturdiness, and good antenna.
I also bought the car mount, the cigarette lighter cord and the Western US Topo software.
I actually used it to help me navigate in Panama a few weeks ago, although the maps of that area were pretty basic. It got rained on, dropped in the mud, etc. with no setbacks.
The problem with using any of these units for in car navigation is the size of the screen. It can be tough to see them clearly at times which could present a safety hazard if you were trying to read the GPS screen rather than watching the road.
I have done limited navigation with it in the US, mostly just for fun. A GPS unit and a real map is still the better way to do it.
I bought mine through gpsnow.com who had pretty good prices and speedy shipping.
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Chris Harrison