I've never used it, but I've heard of the resource below:

http://www.freecampgrounds.com/

On Wed, 11 Aug 2004 01:10:54 -0400, Kim Brennan <kimbrennan@mac.com> wrote:
> So, as I was traveling the last time across country, I realized that
> the map makers put camping symbols on PAY camping spots. But as we all
> know there are other LEGITIMATE spots to camp (no facilities, just a
> spot to park).
>
> Does anybody know of a resource that has documented these? Maybe I'll
> start to do so.
>
> For instance. In the George Washington National Forest (Virginia and
> West Virginia) there are many fireroads and jeep trails. Camping is
> permitted along many of these (and some are better than others. I
> particularly like Meadow Knob (on top of a ridge, a bit away from where
> a lot of hunters or fishers camp.)
>
> In the Monogehela National Forest there is a pay camp site in the Dolly
> Sods Wilderness area (12 sites which quickly get occupied). However
> there are also a couple of road side camping areas which cost no money.
> A few weeks ago I was the only occupent of one of these. I was about
> 150 feet away from the main road in a nice quiet forested area (down
> from the top of the Dolly Sods).
>
> I'm sure there are other similar sites in other National Forests. Of
> the above two sites, the Dolly Sods site is easily accessible by 2wd
> Westys. The GW site is a bit further off the beaten trail and goes over
> some VERY rocky terrain that might frighten away the average 2wd
> person, but is easily reached with a Syncro Westy.
>
> How many National Forests are there? Anybody know (California seems to
> have dozens).
>