5 Nights in Atlanta
Agave for excellent southwestern and great margaritas.
Mary Mac's Tea Room for good southern (it has a lot of Atlanta tradition going for it).
Panahar for Indian/Bangladeshi.
So Kong Dong for Korean.
Woodfire, mentioned before.
Restaurant Eugene, mentioned befor.e
5 Seasons Brewing for superb beer and really good food, too.
Nam, for good somewhat upscale Vietnamese.
Co'm Grill for a different take on Vietnamese.
There's plenty more. Atlanta has a lot of good restaurants.
I agree with the other responses and would add: 10 Degree South for upscale South African; Nan for upscale Thai; Kyma for upscale Greek; the Dining Room at the Ritz Carlton Buckhead (just up Peachtree Street from your hotel) for ultr-luxe dining (one of 15 Mobil five-star restaurants in the country for 2006).
If you visit Atlanta, you must visit The Varsity. It's not fancy but it is, for lack of a better word, the heart of Atlanta. It's downtown across from Ga. Tech. I have grown up on the Varsity food so I am a bit biased, but it is an experience in itself just to be there. GOOGLE choppedonion.com for a review and pictures of The Varsity. This may not be the most popular suggestion as far as other Chowhounds will view it, but its one of those places you need to visit at least once in a lifetime. They do take VISA!
I would get out of Buckhead a night or two. Floataway Cafe is one of Annie Quatrano's places and is fabulous. Midtown is the most happening area. Try The Globe or Ecco.
I would skip ethnic in Atlanta though Buford Highway has many to choose from.
We have an amazing Italian restaurant, Sotto Sotto, in Inman Park if you are in the mood for pasta.
I'm suprised you say to skip the ethnic. Buford Highway, although not scenic, has a lot of great ethnic eats. Try Dai Loi II for pho, and El Rey De Taco for Mexican. Happy Valley and China Delight (which is not on Buford Hwy) get raves for intown dim sum. Lots of folks like Woodfire Grill for more upscale, California-style cuisine. I'd personally avoid Rathbuns and have had a bad experience at Eugene, tho folks love Eugene and they did send me a gift certificate because I wasn't happy with our meal. For high-end I still prefer Joel.
If you are serious about ethnic food, do a search here for Steve Drucker and heed his recommendations about Tasty China, even though it would be a bit of a hike. The chef there has some amazing Chinese credentials.
Midtown is certainly happening, but in a trendy sort of way, IMHO. Think loud, see-and-be-seen restos.
If you give us a bit more specific info on what you are looking for, I am sure we could be very helpful.