What's the main attraction of South Carolina?
In addition to Charleston, I'll throw in a homer vote for Columbia. USC's campus is nice:
Riverbanks Zoo and Botanical Gardens is considered the best zoo in the Southeast and one of the best in the country
The South Carolina State House is historic and beautiful (the columns on the portico there are the tallest monolithic columns in the US - look out for the bronze stars on the western side of the building where cannonballs hit it during the Civil War)
There's whitewater rafting to be had on the Congaree River
Oh and speaking of Congaree there's also Congaree National Park which features some really cool scenes, kayaking, and on summer evenings there's frequent/prominent firefly displays (which lend their name to the local minor league baseball team)