any of the Buckhead Life (I like Chops the best) places are amazing and any of the Concentrics (I like Two Urban Licks) are also.

http://www.buckheadrestaurants.com/index2.html

http://www.concentricshospitality.com/

If you like Sushi, Starfish is amazing, affordable and low key (but not fancy at all):

http://www.starfishatlanta.com/