What are you traveling in, do you like back roads, what do you like to do, and how long do you have?
I81 with a few stops at VA state parks and TN COE parks if you like major roads or in a hurry.
If not and you don't mind back roads, after Shanadoah, hit Seneca Rocks in WV, visit the National Radio Astronomy Observatory, then when the Monongahela NF runs out, swing over to New River Gorge for some free camping (though lots of trains across the river). Finally, back roads over to Cumberland Gap NP. The scenery and NF campgrounds in the area are very nice.