Before you arrive, I would check the concert schedule to see who's playing. There are a lot of options there. I like the Variety Playhouse for the ratio of boho hipness to audience size.
Are you into the Civil War at all? If so, lots of sites to check out, particularly to the northwest of the city proper. A hike up and down Kennesaw Mountain is a nice little workout.
In a similar vein, Stone Mountain is just east of the city. I haven't visited it.
To the west of the city 5-10 miles, you have Six Flags Amusement Park.
If you have a whimsical side, try to make a pilgrimage to the Big Chicken in Marietta.
If you like waitresses with large breasts, the Cumberland Hooters is the "flagship" restaurant for the chain and often has the creme de la creme serving there.
If you rent a car, you will want to be careful on 285, 75/85 (middle of the city), 85 (as it crosses 285 at "Spaghetti Junction"), and 20 (where it crosses just north of the airport). These interstates can all be quite hellish at rush hours; the lanes on 75/85 are particularly tight, and 20 has a vestigial shoulder that people still insist on parking on, causing tense moments for drivers in the passing lane. Also, keep an eye on the weather -- if heavy rain is predicted (or looks imminent) try to avoid 285, since it curves a lot and the lanes quickly disappear in washout conditions.
If you intend to stay in the city:
* if you're going to be downtown and have extra $$$ for lodging, consider the Marriott Marquis -- it's a really impressive hotel;
* you can probably get around fine on MARTA, which is run quite well. Like any major transit system, you need to be a little more careful at night;
* the Midtown (*not* downtown) area has a really interesting feel to it, with small clubs, shops, etc., and neighborhoods with actual lawns.
And I'll add that I think the airport is really good, especially for its volume. Excellent dining options, shopping opportunities, and people-watching experiences :->.
Kevbo