One of the fun and flavorful places to hit when you are in Atlanta is Fat Matt's Rib Shack...a small 'hole-in-the-wall' joint with smoking BBQ and even tastier tunes.
Basically, you order your food (BBQ chicken, ribs, and pork with your standard array of sides), beer, and then grab a seat. A live (generally local) blues band plays each night, providing a nice groove to chow down to.
The place is strictly SRO, and as once the band heats up, and can be hard to find a place to sit. So get there early, grab a seat and some great ribs, and enjoy!