I have been using a Garmin GPSmap60CSx for many years, with grest results, while hunting and hiking. But the screen is too small to use in my jeep while traveling the back country.
Is there such a thing as a dash mounted unit with a screen large enough to be easily seen while bouncing on a Jeep, and with a topo capability at least as good as that of the 60CSx?
The Montana is worth a look. 4" screen is much larger and much higher resolution than your 60csx. I have a 60csx, Oregon 400t, Montana 600 and several Nuvi's. The Montana is my favorite Garmin model ever - has advanced features not found in any other series. The screen is beautiful and it renders topo maps in the "classic" Garmin style, which is great. Works in both landscape and portrait orientations also. It is the most customizable product that Garmin ever made.
https://buy.garmin.com/shop/shop.do?cID=145&pID=75226
If you want an even larger screen, you could look for a nuvi 5000, which was discontinued a couple years ago. I have one of these too and it does a pretty good job with Topo maps (unlike more recent nuvi's that really mangle some things). It will not have the advanced features of the Montana though, also no battery so it only works from vehicle power.
For a still larger screen, you need to "roll your own" and run either Garmin MobilePC or nRoute on a tablet computer. This gets a more complicated. Here's nRoute with one of my own maps on the HP Slate 500 (Windows 7 based 9" tablet).
(http://stephencreek.com/lgpsw/slate01.jpg)
And this is a custom install of Garmin MobilePC with one of my maps
(http://stephencreek.com/lgpsw/mod01.png)
All things considered I would recommend the Montana, due to the advanced features and the fact that it is equally at home for travel on foot.
Nice tablet mount, Boyd. Who makes it?
Also, if one were to have a public domain routable map (like OSM), would MobilePC or Nroute support spoken directions from the tablet?
I made the mount from old junk I had laying around the house. :) Have never used routable maps with nRoute. It's not compatible with City Navigator NT, but there's a utility program to fix that. nRoute is an off-shoot of Mapsource that supports realtime display. It accesses the same maps you have already installed in Mapsource. This differs from MobilePC which uses compiled mapsets like a standalone GPS (gmapprom.img and gmapsupp.img).
MobilePC is pretty much like a Nuvi that runs on a PC. It was recently discontinued but you may still be able to find it. It includes a copy of City Navigator. Not so optimal for topo maps right out of the box, but adding a simple custom .typ file fixes most of the problems (mainly to define thin contour lines because the default is really fat).
I wrote up my impressions MobilePC here: http://forums.gpsreview.net/viewtopic.php?t=23202