Lots of BBQ joints, lots of seafood. Stay away from the chain restaurants and you can't be far from wrong.
If you go out to Edisto Island, stop by Bobo's BBQ by the Horizon gas station. They are only open Thursday-Saturday evenings. Great BBQ.
You can also try Flower's Seafood about a mile from Bobo's. You'll have to eat at a picnic table outside, but great local seafood. Usually straight off the Flower's boat.
If you get by Summerville, SC, stop by Oscars for dinner. Don't order off the menu, get whatever is on special. Not cheap, but great food.
Cheap seafood, go to Gilligan's. Decent food, reasonable prices and they only serve local seafood rather than Vietnamese or South American imports.
If you want a sushi shop, stop by Sushi 101 in Goose Creek. Probably my go to spot for a dinner out. Get a sushi roll and a plate of veggies or hibachi steak and chicken. Good stuff. Oh, and the Beef Tataki is to die for if you like raw beef.
For over the top expensive but outstanding, try 82 Queen or High Cotton. It's been a while since I have been to either of those, but they used to be some of the best in town. I prefer Oscars. They are less pretentious.
If you are passing through Georgetown, SC around lunch, stop by Nagoya in the Walmart shopping center. Great hibachi style food, reasonable prices and probably more than you can eat.
If you are flying up I95 and want lunch around Santee, SC. Try Clark's Inn and Restaurant. We make a Sunday afternoon trip every couple of months for lunch. Nice drive, good food. The only problem is wanting a nap on the way home.
Last one. If you like diner food, hit Alex's in Goose Creek or Flower Town in Summerville (same family). It's diner food, what more can be said. Some times it's just what hits the spot.
That's all I can think of at the moment.