Here are a few ideas and I also included places to sleeping in your car.
CAMPGROUNDS AND CABINS
-Camprounds and RV Parks : http://www.campusa.com/
-Campgrounds directory :
-The Campground Network : http://www.the-campground-network.com/
-KOA Camprounds directory (usually between 20-35$): www.koa.com
-National Parks, National Monuments and State Parks : http://freespace.virgin.net/john.cletheroe/usa_can/natparks/index.htm
-Bureau of Land Management campgrounds (usually between 5-12$) : http://camping.about.com/cs/campgrounds/a/public05.htm
FREE CAMPING/SLEEPING IN THE CAR (in other words if you like adventure):
-Strange places : www.sleepinginairports.net/strange.htm
-Long term visitors areas :
**Don't forget to ask for a free directory it's always practical to have it on the road.
-Flying J : www.flyingj.com
-TA Travel Centers : www.tatravelcenters.com
-NATSN : www.natsn.com
-Pacific Custom Brokers : www.pcb.ca