There are plenty of places to ride in Atlanta. It depends on what you are looking for. I think that the best option for a visitor who is not so familiar with the city would be to ride on either the Silver Comet Trail or the Atlanta/Dekalb trail system.
You can find info on both of these on the PATH foundation website: http://www.pathfoundation.org.
If these paths aren't quite what you're looking for, let me know and I'll see what I can do to help out.
Beth