the top of the Westin Peachtree (the top two floors rotate - one's a lounge, one's a restaurant, but for $7, there's a look and see level, which is great on a clear day)
Just a tip...you may want to check and see if this is still an option.
I was there recently and you can still go to the top and view they city. I'm not 100% sure if the restaurant still rotates since I wasn't really paying attention. When I went they used different elevators to the top that you could not see out of.