25 Andrew Young International Blvd, south face of Peachtree Center. This is the real gem of my downtown Atlanta experience, and if you have just one open meal, I really think it's worth going here. Bring the gang. They have some great entrees, including grilled fish and a nice bacon-wrapped filet mignon, but I keep coming back to the Plantation Combo, a ribs and fried chicken platter.
The pecan crusted catfish appetizer is awesome, but the "sideboard," or salad bar on steroids, that comes with every entree, means I almost always skip the appetizers unless I have several friends around to share them with.
231 Peachtree Center Ave, east face of Peachtree Center Mall building, next to Benihana. Really just in the mood for a burger? This pub has lots of good beer on tap (I suggest the local Sweetwater brews), and great burgers and chili. I suggest putting them together.
Corner of Courtland and Andrew Young Intl Blvd. This is really just a fast food gyro joint, but if you find yourself needing lunch downtown, it's a great choice. They're pretty quick and the gyros and burgers are excellent.
Other good options, both by the corner of Peachtree Center Ave and Andrew Young International Blvd, are Mama Ninfa's, a good Mexican place, and the Metro Cafe Diner, which has great diner breakfasts, and if you're up really late, is open 24 hours.