Wild Geranium -- Geranium maculatum -- tends to be a low-mounding or groundcover, blooms in spring to summer, fall color is good
Wild Columbine -- Aquilegia canadensis -- spring bloom, wiry stems and open foliage, will self sow to peak up among groundcovers
Sprengel's Sedge -- Carex sprengelii -- about 2' tall when in bloom each spring, greens up early for a grass-like appearance
Ivory Sedge -- Carex eburnea -- low mounding and super soft groundcover that slowly spreads its clump
Early Meadow Rue -- Thalictrum dioicum -- cool, tiny, round leaves with 2-4' spikes of orange-ish / yellow-ish blooms
Poke Milkweed -- Asclepias exaltata -- 3-5' tall with cream to white bloom sin early to mid summer
Calico Aster -- Symphyotrichum lateriflorum -- tons and tons of white blooms with centers that turn from yellow to pink, about 2-3' tall & wide
Zigzag Goldenrod -- Solidago flexicaulis -- highly fragrant creeper reaching about 3' tall with thick, serrated leaves
Read more about each of these plants via their plant profile articles, and explore other pieces on gardening in shade.