Not sure about Savannah but if you head down 17 South to Shellman Bluff I hear nothing but good things about Hunter's Cafe. It's down by the marina.
Also if you make it that far then the 50th Annual Blessing of the Fleet is all weekend in Darien. Lots of things to do and see. And Skipper's on the river in Darien is very good.
Hunter's is the best -food and ambiance.