Not being from your part of the country, I am not going to suggest specifics but first, see what your native ferns are in GA - always a good place to start. Next, what size to you want? Tall or short? The ones that really want it wet are the osmundas but most ferns want some moisture. You've got lots of choices with your zone and I don't know that the heat will be too much of a factor since the spot is shady and moist. Read posts of favorite ferns for ideas... Just buy some, you'll get hooked and need more.

Ferns native to Georgia? Here's a short list:

Christmas Fern (good for dry areas)
Ebony Spleetwort (good for dry areas)
Lady Fern
New York Fern
Hay Scented Fern
Cinnamon Fern (good for wet areas)
Royal Fern (good for wet areas)
Netted Chain fern
Sensitive Fern (good for wet areas)
Northern Maidenhair fern (gorgeous!)
Broad Beech fern
Southern Wood fern (Thelypteris kunthii)

Ask at the garden center if Autumn Fern or Japanese painted fern will grow in your area. They are beautiful and add the color you are wanting.

esh_ga, which ones of those natives that you listed are tall/ reddish? I definitely need taller ones to stand up behind the hostas.

I've got both Autumn Fern and Japanese Painted fern in other places, and I agree they're beautiful. How tall does the painted fern get? Mine are still little, but they're in a woodland with less moisture than they would get near the ditch.

Lady Fern can have reddish stems (especially if you get the "Lady in Red" cultivar available in nurseries now). I have some naturally occuring clumps that get 2 1/2 to 3 feet tall. Royal fern starts out with purplish fronds, but it does not hold the color. Northern Maidenhair is the same way, reddish on the new fronds but then green. Sensitive fern has a reddish tint also, but can be aggressive in moist conditions (you might like that trait!).

In the Japanese painted fern family two varieties that I would suggest for contrasting foliage would be "Ghost" which as the name leads you to believe is nearly silver and really lightens up a dark corner or "Ursula's Red" which has a nice grey/green frond with a burgundy stripe.