There are two that are worth it: either McCrady's, as HellsSoxHound mentions, or Fulton Five.
Just as a side note, a lot of the splendor of Charleston rests in the "downhome" charm of the place. Thus, a lot of the best meals can be found in more simple joints, as opposed to the overpriced, over-hyped restaurants.
Cru Cafe (right off the Market) is one in particular...
i have a really lengthy post on my honeymoon from charleston a few weeks ago...
if money is no object, then the ocean room was awesome...
one that we really wanted to try but didn't was cordavi--that menu looked really good. another was mccrady's, which was a little too avant-garde for my wife's tastes.
have fun--it's a great city!