I was just alerted to this site, and I'm already finding great joy in using it.  It's great for finding free/cheap spots to overnight at, such as when you're in transition to your next destination.  My biggest complaint with site's like freecampgrounds.com was that you couldn't see the sites on a map - which if you're like me when in transit, you don't always know all the local towns around you.

With this site, you just key in a major town you do know, click your radius of search and it comes up with all the places folks have found in the area to overnight. It tends to include retail shopping places that allow overnight parking, public campgrounds, etc. And it has excellent details and directions, and even includes places that don't allow parking.

It does cost $17.95 a year to join (heck, if you get just one free night of camping out of it instead of paying for a campsite, you might just be ahead!), however you get a 2 week free extension each time you contribute information to the database. 

Check it out..   http://www.overnightrvparking.com

 - Cherie