Deleware Seashore State Park is right by the ocean, and right on the Indian River Inlet. The park itself isn't much, but the location is great. No trees, you are out in the sun. Easy access to ocean, river and nearby beach towns.
Cape Henlopen State Park is a little further north on the Atlantic Ocean by the Deleware Bay. Nicer park like setting nestled in pine trees. A little longer walk (couple minutes) to the water, but easy access.
Camp Hatteras in NC is pretty nice. We are going there next year, but a camping friend was there last year. The ocean is literally on the other side of the dune from the campground. Again... no trees in the summer.