Awesome progress with these maps. I figured I''d C&P some of the most useful links here.

First, using satellite & shuttle imagery, USGS brings you this nifty web tool that lets you quickly render & view ections of the United States (note it says world also, but there is really nothing in the way of data outside the US on it).
http://seamless.usgs.gov/

Lots of good files here, including some free lower res DEMs, you can get bulk deals & CDs for low cost as well with membership.
http://data.geocomm.com/

These are topos you''d use for hiking, but the grid helps you match up downloads from geocomm
http://www.topowest.com/

This is a random terrain generator, good for making terrain if you don''t want to rely on nature & USGS.
http://www.planetside.co.uk/terragen/resources.shtml

And for viewing DEMs & a few other formats, this viewer is a free download with limited functions. If you register you get more functionality (like loading more than 4 DEMs at a time, modifiations to maps etc).

Again, I gotta thank you for that link. Now if I could find a script to import these into Gamebryo...