well, your best bet will always be native plants-you might want to take a hike through the area, and see what WANTS to grow there. Irises tend to do well- as do the 'road lillies' if they'll survive that far south. I seem to remember bouganvilla growing quite nicely over an arbor that got seaspray several times a day...

and there's a thing called a 'sea pink' that's a little cushion of green that sends up little pink pom-poms that will grow in dunes, you might want to see if you can find them.

Have you checked out the Southeast Coastal Gardening Forum?

Teri

Trees--Sea grape(coccoloba), Conocarpus, shrubs--suriana, scaevola, groundcover --phylla or lippia, Vitex rotundifolia. I am assuming that you are in south Florida. Good idea about checking out the natives.