Some barrier island information on the web (a few selections from the MANY hits you can get from Google or AltaVista).
A nice introduction to barrier islands from HowStuffWorks.
A guide to the North Carolina Barrier Islands.
A tutorial from Salem State College (with a self-test based on Plum Island).
A teaching guide from the US Geological Survey (USGS).
Mary Edna Fraser's homepage, with some of her online batik images of barrier islands from the book 'A Celebration of the World's Barrier Islands'.