I always carry the Woodall's Directory just in case I have little or no internet connection. Otherwise, any or all the websites posted are great resources.
Seems like several posts have come up recently regarding trip planning. Ah Spring! I have Streets and Trips and I use several of the camp finder search tools mentioned in several other replies, but I find it VERY helpful to be able to identify camps along my route as I plan. Recently, I have been making more use of a website based planner called RV Trip Wizard. From info on the website, the developer is an RV'er, the database is extensive, they are providing a way for campground owners/operators to keep their info current themselves, and I have been able to use it on the road via cell phone hot spot. Check it out.
I bought the Woodall's Western Campground Directory and it was a waste of money. The campgrounds are listed alphabetically which is terrible when trying to find a campground in an area where you plan to travel. If you do not already know the name of the campground you are not going to find it with this directory. If you plan to travel to New Mexico and want to find all the campground along the way to Santa Fe this directory will not get you there.
The Woodall's listings are so cursory as to be worthless. They provide less information than one can get from state parks or national forest service campground maps. Comparing their entry for the campground at the state park near San Simeon, Woodall's states that it has 115 sites with 35 maximum RV length, tenting, dump, saltwater swim, ramp, saltwater fishing. No mention that the ramp is only adequate for hand launching of very small boats or how many sites are for 35' RV's.
By way of comparison the listing for the same campground by Stienstra mentions that that Hearst Castle is only 5 miles to the north and provides the phone number for booking a tour, Mentions a second San Simeon Creek campground across the highway and also the Washburn campground further up the bluff with more privacy and better views of the ocean, He mentions the best hike from Leffingwell Landing to Moonstone Beach, that from the bluffs it is easy to see passing whales, that there are 3 preserves in the park, including a winter nesting site for monarch butterflys and an archaeological site dating back 5800 years, that in the summer there are junior ranger and interpretive programs offered.
Writing about the campsites in addition to the information in the Woodall's Western Campground Directory listing, Tom adds that picnic tables and fire grills are provided, drinking water and coin operated showers are available, firewood is available at Washburn, a grocery store, coin laundry, gas station, resstaurants, and propane gas are two miles away in Cambria, that some facilities are wheelchair accessible, pets are permitted on a leash. Stienstra provides period during which reservations are accepted and the phone number for them, site fees at San Simeon Creek and for Washburn, additional vehicle charges, directions to the park and the phone number for the park.
With Tom Stienstra's California Camping guide the campground listings are broken out by geographic section and each section has its own set of maps to make it easy to determine the layout and travel logistics before arriving in an area.
I also make use of the excellent National Forest Service maps which are better and cheaper than the ones from the map companies and the forest service maps include all the roads in an area including the unpaved logging roads in the west.
For anyone traveling around California the Tom Stienstra book is a great resource for not only finding campgrounds but for doing your trip planning so as to have as pleasurable a time along the way as possible. And no advertising - none!
I use the internet for finding the least expensive diesel and for making reservations but it is a time vampire when it comes to trip planning with all the commercial sites.