The Terrapin Rye Pale Ale has to be in my current top 10. Sweetwater is also very good.
I am from Atlanta, but currently live in Tampa, and our world-class brewery, Cigar City, is distributed in Atlanta. If you've never had any of their beers, you need to. I would put them up against any of the best breweries in the whole country. Jai Alai is one of the best IPAs out there. They have a fall seasonal Farmhouse Ale called Sea Bass that might be my favorite all-time beer if you can find one. The Tocobaga Red Ale is also probably my current favorite red, if you don't count Rodenbach Red (a Flanders Red).
As far as brewpubs/breweries:
5 Seasons Brewery has three locations, and is a really nice brewpub that makes their own organic beers.
The Vortex in Five-Points has a great draft and bottle selection and is a very unique, quirky restaurant with GREAT burgers.
There is a Gordon Biersch brewery restaurant in the Peachtree Street/Buckhead area and the Midtown area. Get the das boot!