I also hang out on the Adventure Rider site - lots of great travel reports and pictures there.
Two of the regulars just completed a ride from the Arkansas border to the west coast on the TransAmerica Trail - spectacular scenery through the middle of nowhere - see link here:
For those of you who haven't heard of this - it is a mostly dirt (96%) route mapped across the country from central Tennessee to the Oregon coast. Its the work of Sam Correro and the route can be purchased from him at his website:
I contacted Sam not too long ago and he responded that 98% of his route could be done with a well equipped four wheel drive expedition vehicle - there are only a few stretches of single track on the whole route - most of it is farm roads, single lane dirt roads and off road tracks. His maps offer alternate routes around bad sections and the reports I've read of those who have traveled on this trail have been spectacular. Picture 3500 miles of off-roading across the USA. It would probably take three weeks to properly run the whole route but a lot of guys on the ADV site do it state by state.