Someone mentioned Camping Life Magazine from Woodall's so I went to their website and found this great list. Be sure to go to the article and read about each campground, as there are some great ideas there!
25 GREAT BEACH CAMPS
http://www.campinglife.com/output.cfm?ID=1269415
WEST COAST
Fort Flagler State Park, WA
Cape Disappointment, WA
Nehalem Bay State Park, OR
Oregon Dunes National Recreation Area, OR
Carter Lake in Oregon Dunes National Recreation Area, OR
Gold Bluffs Beach in Prairie Creek Redwoods State Park, CA
North Beach Campground in Pismo State Beach, CA
Oceano Campground in Pismo State Beach, CA
Oceano Dunes State Vehicular Recreation Area, CA
El Capitan State Beach, CA
Refugio State Beach, CA
Leo Carillo State Beach, CA
San Elijo State Beach, CA
GULF COAST
Padre Island National Seashore, TX
Mustang Island State Park, TX
Grand Isle State Park, LA
Gulf Islands National Seashore, MS-FL
St. Joseph Peninsula State Park, FL
Bahia Honda State Park, FL Keys
ATLANTIC COAST
Cumberland Island National Seashore, GA
Cape Hatteras National Seashore, NC
Kiptopeke State Park, VA
Assateague State Park, MD
Delaware Seashore State Park, DE
Hither Hills State Park, NY
Rocky Neck State Park, CT
Cape Cod National Seashore, MA
Nickerson State Park, MA
Lamoine State Park, ME