I don't know much about rain gardens, but it sounds like that's what you've got:
http://learningstore.uwex.edu/pdf/GWQ037.pdf

And have you asked at GW's Carolina Gardening forum? They might be able to help you with plants suited to rain gardens in your area.

Check out vernal pools. Might be some natives in your area.

Many pond marginals can handle wet followed by dry. The duration of dry can be an issue, so you might have to add water during dry spells. Or let the plants die back and they will pop back up when water comes.

Here in Phoenix humidity is often under 10% in the summer and temps well into the 100's everyday. Yet many pond marginals are used a lot here in landscape because they can store water thru the dry patches. Canna, rubella and papyrus are common here. Actually several sedges are common, brown nut sedge is considered a weed but I use it as a landscape plant. Any plant that stays green thru our summer with little water is a good plant in my book. You probably have several native sedges to chose from. I do keep mine inside a bed with a liner so they don't get loose.

If you want spectacular check out Giant Reed, Arundo donax. May be outlawed in your state so check that out first. Makes bamboo loot like a slow grower. You really have to stay on top of it, digging a lot out every year. But an impressive plant.

Almost all marginals can be grown in wet soil and do better than if submerged. When plant guides say 6" of water they're referring to the max amount of water they can take so do not actually have to be submerged.

Like missingtheobvious, I suggest you check with the Carolina forum. Unfortunately, it is not very active, but on the bright side, the most vigilant and knowledgeable person lives in Raleigh.

I am also nearby in Pittsboro. If you want to learn about native plants, you might want to come west (south of Carrboro) and visit Niche Gardens. It specializes in natives. I think the river rocks with small plants would work well. However, one problem is that this area can go for prolonged periods of dryness. When we got here 10 years ago in mid January, there was a significant stream flowing across a semi-lawn. We had thoughts of creating something similar. Fortunately, we were too lazy/busy and while the stream reappeared moderately the next year, for most of the year it was totally dry and in subsequent years, the stream almost never appeared at all.

Thanks for the link, missingtheobvious. that's a great guide. Sounds like a rain garden is what I want. I'll follow up in the thread you recommended for plants etc specific to NC.

Waterbug_guy, thanks for the suggestions. I'm trying to keep everything here native though.

Thanks chas. I have heard a lot about Niche gardens and I will check there too.