I second the Delorme TopoUSA idea. I picked up an older version for $20, and it was about the best 20 bucks I've spent on touring gear. Before our tour last summer I spent 5 days or so laying out routes, generally following AdventureCycling trails. And printed out two sets of handlebar-bag maps for the entire trip (US part, anyway). The maps show elevation, topography (great to know the names and directions of natural landmarks), public/private land, as well as towns, etc. I love maps with shaded relief features because just a glance gives you a lay of the land.
What Delorme TopoUSA doesn't show is campgrounds. Ironically, I used a set of Delorme paperback state maps -- the standard before software came along -- for this info. These maps are even better than their software, but of course not in "portable" form. They show every public/private campground, and I transferred these marks to my printed maps.
As supcom says, traffic data is a bit harder to come by. You start to get a feel for that in each state you pass through, by paying attention to shoulder quality, main vs. alternate routes (the map is invaluable here), asking locals.
-- Mark