For good advice (from my personal experience):
Tim at Keen Reef (Decatur area)
Chris at Fish Scales (Buford/Suwanee area)
Jenn at Imagen Ocean (Canton)
John at All Things Aquatic (a bit of a drive in Hiram, but John is very knowledgeable and from what I hear he has a great store)
I've also heard great things about the people at Creation Reef and Pure Reef
For great displays:
Pure Reef (Alpharetta)
Marine Design (Alpharetta)
Marine Fish (Marietta)
Warehouse Aquarium (two locations)
Einstein Acquatics (Tucker)
Again, this is my personal experience and others will have different stores they like, however, the two lists above are probably the most mentioned stores on the site. I think most of our sponsors will give you good advice, however I have had bad experiences at a couple. The map is helpful as far as looking for stores in a certain area. Find a store you think you might want to go to, then take a look at their sponsor page and read some of the forums. You should see threads of people leaving feedback on their experiences.
I also try to look at the sponsors that are most active on this site (John, Chris, Jenn, Tim, and a few others). And not just active in updating their promotions, but really try to help out, and these people do!