In addition to Wednesday WindDown, I have two suggestions:
Lunch on Broad -SunTrust Lunch on Broad takes place every Friday, weather permitting, Enjoy lunch with your friends along with free live entertainment. May 2 through September 26, 2008. noon - 1:30 p.m.
and
Wednesdays in Woodruff - Starting at 12:00 noon every Wednesday in April and May and then in September and October, performance groups will entertain lunchtime crowds in Downtown Atlanta’s Woodruff Park.