The region of Zeeland in South Holland has quite a few camping sites close to the beach.
Haamstede and Renesse are areas I am more familiar with, and they have nice beaches which aren't usually too crowded.
Nearby are also some beautiful towns such as Veere and Middelburg.
The following website has a fairly useful list of camping sites in the region:
Though I haven't been there myself, the islands in the north are apparently also beautiful. The island of Texel seems to be particularly popular.
Several people have told me its definitely worth a visit, and I have family that go there every year and they strongly recommend it. about 11 years ago