Here are some rides that are closer to home and (if you live in the Atlanta area) could be done without staying overnight:
Beautiful Backroads Century on September 17. It has a 12, 27, 45, 65 and 100 mile routes. There are a few short and steep climbs, but it isn't too challenging. Although I have heard that the century route has more challenging hills. This is a very popular ride and is well attended every year (arrive early to get a decent parking spot). It is also well marked and a popular route for local cyclists to use on the weekends. Starts at the Anheuser Busch plant in Cartersville near I-75 exit 296.
Cartersville Century (already happened this year, scheduled for late June). Has 15, 30, 50, and century routes. This is one of my favorites. The 50 mile route is enerally flat with only one challenging stretch. Don't know about the 100 mile route. Good one to keep in mind for next year.
One that I like doing in the spring is the
Rose Pedal. Has 27, 43, 63, and century routes. For the past two years this has been my first organized ride of the year. It's a bit more challenging than the BBC, with two tough climbs on the 43 and 63 mile routes. The second one can be easily bypassed if you're not up for it. Starting point is in Cumming. This route isn't as scenic as the others and the roads tend to be more crowded with automobiles. Usually the second Saturday of April.