The Netherlands has a good few comping spots that, I am told, are completly free. I have not yet been to any and this is why I have not posted them as camping spots yet.
I will be checking them out one by one soon as its not more than a 4 or 5 hours drive from me.
Each one is acompanied by a sign that looks like this...
http://www.lekkerweg.nl/nl/system/Images/paalkampeerterrein_560x350_tcm4...
( a picture of a backpacker, a tent and a sign. Underneath the sign is a list of the facilities available. (mostly just water pump and a bench)
They are there for cyclists and backpackers and they are completly free.
Here is a link to a map show (I think) all of them. It might only be a select few, I dont know.