There are many different sizes and textures. Astilbes come in many colors and sizes, Bleeding hearts, Japanese Anemones, Wild Geranium, Coral Bells, Celadine poppy,Goatsbeard,Columbine, Queen of the Prairie, Monkshood and one of my favorites, Virginia Bluebells. For spring color, think Woodland. Jack in the pulpit, trillium, Dutchmen's breeches, violets, toothworth. If there is a tree shading your garden, in spring while the leaves are still not out, you can plant spring bulbs for color.
Shade gardens can be a welcome spot come summer.
I have a small table and chair in my side yard shade garden and it is one of my favorite places to sit on a hot summer day. One drawback is I sometimes have a slug problem because of the damp cool environment. Hope this helps. There are some great shade gardening books out. Go to a book store that sells coffee, curl up in one of those nice chairs and look through shade garden books.