What type of camping are you looking for? RV/Camper? Car? Back country?
Map of Free Camping Areas | Go Camping for Free! is a listing of various no-fee and usually no-amenity sites around the country; with many along the Blue Ridge and in the national forests.
Ncparks.gov - you can check out the parks and reserve campsites online.
some of the other campsites are run by the us forest service and us parks department. You can check out their websites as well.