Gardening--Gardening in Georgia is a popular hobby. Many people get help from Walter Reeves who is on WSB radio and PBS television. His website will keep you up-to-date if you miss his show. His radio show Saturday morning takes phone calls. Here is his website. http://www.gardeningingeorgia.com/
If you are really serious about Gardening you might check out the local Garden Clubs.
Gaming--By gaming, we mean board games like Monopoly and role playing games(RPG) like Advanced Dungeons and Dragons(AD&D) and war games like Warhammer.
For Fantasy and Science Fiction alike check out DragonCon.org. The DragonCon Convention is held in Atlanta every year around the Labor Day weekend. It is usually in the Hyatt Regency, the Marriott Marquis, and the Hilton in downtown Atlanta with a parade including Storm Troopers down Peachtree Street.
Hiking and Camping---This may not be considered a hobby by some but it is certainly a well represented activity on the Atlanta Clubs page.