I suggest possibly a trip to the Georgia Perimiter Botanical garden. They have damp shady locations, and damp sunny locations - that might be a good help to you.

Ajuga or bugle weed as it's also know works great. I've planted it in fully shaded areas where it grows wonderfully. It will grow fine in partial shade as well. I planted some beneath my river birch on a slope and it's held on and started to spread. As its spread I've taken smaller plants from the original and moved them to further protect against erosion. The plant has down well and has great spikes of purple flowers in the spring. All the plants have held their ground during the tons of rain we've had. Reminds me I need to go propagate some more..!

I second ajuga. In shady wet spots it does wonders, and multiplies very well. Easy to transplant, too.
~Natalie

Can you plant it alongside perennials? Without fear of it taking over?