Hi Chris -- probably your best source of group rides (road) is
www.bikesbl.org for the Southern Bike League. A great group, with a very full calendar of rides. Regular rides are on the calendar, but folks are always just posting looking for others to ride with for an impromptu route. Another site with good maps, but mostly towards the west side of town, is
www.atlbike.org
(Sorry, I'm not a clyde/athena, but the title caught my eye. Hope it's okay that I posted here!)
PW