Another thought or two for Savannah,
Wormsloe Plantation, particularly the long drive down the oak-lined avenue, is as beautiful as the low country gets and it's rarely crowded.
If you're interested in things military, (or just a beautifully preserved bit of 19th century engineering and architecture) drive out toward the beach and visit Fort Pulaski.
And speaking of Savannah's closest beach, Tybee Island is a bit of a throwback... not yet overdeveloped, funky and very, very laidback. They live on what the locals call "Tybee time."
And a second, (or third or fourth!) for Coinneach's recommendations for Molly MacPherson's. Give a post here or in the Georgia sub-forum closer to the day you're in town, and who knows, you might scare up a companion or two for a round at Molly's. The one downtown is in the midst of the Historic District.