I think ajuga would be a nice groundcover and I used to have a purple variety, the foliage was a bronzy purple color, pretty. I should take shade or sun. I don't think it will mind the damp soil either. You might also try creeping jenny. Be sure to choose hosta that will take some sun. Some of them will tolerate quite a bit of sun, others not so much. That may make a difference if you have afternoon sun on this area. Coleus may do well, but it's an annual, not sure if that is what you want.
