I spend a lot of time in Myrtle Beach, which is where I am now.
+1 on Brookgreen Gardens, and Huntington Beach State Park across the road. There's more than just gardens and a beach -- the Atalaya ruins, natural history museum, hiking trails and interpretive displays, zoo, and great boat tours of the marshlands and old plantation rice paddies. Great lunch restaurant at Brookgreen too.
You can keep the rest of Broadway at the Beach, but the aquarium there is really pretty good.
The beach at the southernmost end of Pawleys Island is a really neat spot.