Ooh! I'm glad you asked this! I was eating a spinach salad (store bought) today, and wondered if I could grow my own spinach and when to start.

I'm not a seasoned GA gardener - still trying to figure this climate out. Here are two charts, though:
http://thevegetablegarden.info/resources/planting-schedules/zones-7-8-planting-schedule
http://www.walterreeves.com/uploads/pdf/vegplantchart.pdf

It's been so warm you can plant just about anytime as long as it's not going to be freezing in the next few evenings after planting. The more difficult thing to do would be to germinate the plants. Many need fairly warm soils to germinate. Generally fall and winter plantings happen from August into September when the soils are warm and the sun is still stronger and is offering more sun hours during the day. This helps the seed germinate. But you can plant seeds indoors under lights or in cold frames now, and then plant small plants in the garden. My favorite schedule is from Georgia Organics. It is mostly for the Atlanta region: http://gostaging.digitaltoolfactory.net/wp-content/uploads/2012/10/plantingcalendar.pdf