Tamarind Seed, on Peachtree, is one of the well known Thai restaurants in town. The proprietor also runs Nan, a few blocks away.
I've been there several times. Today, I tried the flounder in green curry. The fish was perfectly cooked. It had a delicate texture and served to carry the flavor of the curry. The curry itself was rich without being ridiculous and just the right amount of heat for me. Their signature dish is the fried fish wrapped in a spiral, which I'll have to have again on another visit.