I love road trips, too. I think planning it out before hand is nice. Do some research, check out google maps, do a state by state check of really neat festivals, farmers markets, outdoor markets, pack well. Camp some and occasionally stay at a hotel so you can feel clean and take a good shower.
We really want to do some kind of train trip this summer. We were thinking of taking one from Seattle to Portland. It's not far but my boys are younger and they really want to go on a train.