Judy, Have you considered some raised beds? Even raising it a few inches woudl help to increase your plant possibilities. Without that how about sedges (there is a nice article about them in this months Fine Gardening magazine) for more perennials also Cimicifuga (Bugbane), Ligularia, Rodgersia, meadow rue. In areas with a bit more light you could use Siberian and yellow flag iris, turtlehead and blue lobelia. Shrubs could be Summersweet clethra, redtwig dogwood, Winter Red holly and Henry's Garnet Itea. Annual cannas will also work in areas with a bit more light.