Decatur is a city northeast of Atlanta that has some good running spots.
Downtown and North of College Ave: This area is north of College Ave. Downtown has some pleasant streets for running. Be sure to run by the Old Courthouse, with the Jefferson Statue in front. Make your way up to Woodlands Garden which has some nice tree-lined paths (use Ponce de Leon Pl./Clairemont to get there).
South of College Ave. Some nice running south of College Ave. The campus of Agnes Scott College is attractive for running, with some pedestrian paths and a running track at the soccer field. The surrounding tree-lined streets are also pleasant for running.