Excellent choices abound. Mine are Collonade on Cheshire Bridge Road, along with Greenwood's on Green Street in Roswell and Veggie's to Go (also known as Chip's Country Cooking) in Sandy Springs on Roswell Road at Hilebrand - behind Dunkin' Donuts.
Rolling Bones has very acceptable bbq on Edgewood near downtown Atlanta. Better is available at Swallow at the Hollow on Green Street in Roswell, and the best is Sam & Dave's BBQ 1 on Lower Roswell Road in Cobb County.
Gotta say I am partial to Carvers on Marietta near the jail. It is more "Down South Homey" than "soul," but it is the best "meat n' two" that I have had in a long time. All the standards are present and when they run out of a dish they just scratch it off the board. I particularly love the collards (tender not mushy), Broccoli n Cheese cass. (covered in broken buttered ritz crackers) and the outstandingly bad for you Hash Brown cass. with salty country ham. It may kill you after two bites but you will go down with a smile on your face. Just be aware that the two house drinks, tea and lemonade, are properly southern strong and may cause diabetic shock to the unaware. Limited hours (11 to 3) or so, and the fact that they can run out of your favorites early are turn offs but the price is right (under 10$). They will be closed next week for vacation but I would hit this one no matter what.
I am sure others on the board will cover Mary Mac's (touristy but a classic) and Thelma's ( I have not been to the new location) and the normal BBQ favs (I am partial to Pig-n-Chik, Lone Star Rib Ranch, Daddy Dz and random road side stands in bad parts of town) but please be aware that the ATL is pretty barren BBQ wise when compared to other major southern cities. Good Luck!