Some of my favorites in SC are Isle of Palms (outside, Charleston) Cherry Grove (north of Myrtle Beach), Fripp Island (outside of Beaufort).
Isle of Palms is an expensive area as far as hotels go - haven't looked into house rentals there. Cherry Grove has lots of rentals - on the beach, on the water way or within walking distance to the beach. Fripp Island is a gated island that is privately owned. I know there, you can rent and then purchase a week membership to the pool at the Beach Club. It has been a while since I was there, but I love it. They have beachfront houses, houses on the waterway and houses on the interior portion of the island. You basically have to drive back into Beaufort if you want real groceries. There is a small market on the island. You can rent bikes, charter fish, play tennis and golf.
I really don't have any rental info I can give you because when at Cherry Grove and Fripp, I have stayed with friends. When we went to the Isle of Palms, we stayed in Mt. Pleasant.