We can't ride the Appalachian Trail or the Pacific Crest Trail, but now we have our own!
Adventure Cycling (the creators of the trail) have a Great Divide Trail summary page and a page with a long article about the trail with lots of details.
A two and a half thousand mile mountain bike trail? This trail nearly follows the Continental Divide from Canada to Mexico (and now extends into Canada!) through some of the most beautiful states in the US: Montana, Idaho, Wyoming, Colorado and New Mexico.
Until i start carrying them, you can get your maps and guidebooks for the trail at the adventurecycling.org/store or an unoffical version at mountaineersbooks.org.
wikipedia article on the trail
Read this incredibly detailed Great Divide ride report with full GPS data and lots of pictures by Scott and Paula.
larger links have more content
All 50 US States