Here's my list from this year:

Raider 48: Has a wide variety of gravel, dirt and a bit of pavement. Really cool climb at mile 41 on a roadway abandoned due to washouts. Has 1-2 creek crossings.
https://ridewithgps.com/routes/12312326

Assault on Mt Currahee: Shares some of the same route with the above but lots of different roads and an awesome dirt climb up Currahee mountain.
https://ridewithgps.com/routes/11895342

Southern Cross: Lots of climbing, lots of dirt.
https://ridewithgps.com/routes/293488

Red Clay Ramble: Flat and very fast.
https://ridewithgps.com/routes/4942068

Sac of Suds 50: Flatter but some short and steep climbs.
https://ridewithgps.com/routes/10979151

I've done all the above on a cross bike and they'll all doable and very fun. I used a 46/36 crankset with 12-32 gearing.

Fried Green 50:
https://ridewithgps.com/trips/2048676

And here's a listing from Bikeforums member TimothyH. If you want to experience some insane climbing and huge chunky gravel check out the Cohutta Wilderness area. It's a blast. Might be a lot of walking on a cross bike though, I rode a hardtail MTB with dropbars and really leaned on my 22/32 gear to get up the climbs later in the ride.

Atlanta Bike Rides: Gravel

This route is also known as the "Cohutta Death March", it is very hard. https://ridewithgps.com/routes/11912075
There's a bit of gravel out near Dallas and some segments near Roswell that you can patch together to make a fun ride.

Let me see what else I can dig up...