I love researching these types of questions. Hope something I find will be of use to you.
Acanthus spinosus - Bear's Breeches: Some types of bear's breeches are hardy to
zone 5. Just be careful to get the right ones. The
flowers are white with purple hoods. If I remember correctly dads bloomed in August.
Acer palmatum 'Atropurpureum'- Maple, Japanese: these are my favorite
trees and they grow so slow that they are more like a shrub. And the leaves are so great that
flowers aren't necessary. Or at least that's what I think.
Monkshood: blooms from mid to late summer. Comes in a variety of blues and whites.
Lady Bells
Bugleweed: These are grown covers for shady areas that you might like. I love the darker ones.
If you can put a trellis up this is a nice vine Chocolate Vine
Anemone crispa - Parsley Leaf
Windflower: Many of these will grow in partial shade
Japanese Anemone: Many of these will grow in partial shade
Columbine: These come in every color imaginable and bloom
spring and fall.
Sea Thrift
Asters
False Spirea: Multiple colors
Masterwort: multiple colors
False Indigo: Multiple colors
Blackberry
lilyPigsqueak: All shades of pink
Chocolate
flowerBellflower: I have some of these in my garden and can't wait for them to bloom.
Red Valerian
Quince: I love quince and it usually beat the lilies of the valley for early blooming when I lived in washington state. But they do have big thorns and they do travel.
turtlehead: multiple colors
lily-of-the-Valley: comes in pink and white
Tickseed: nice variety of colors and shapes
Dogwood, Redtwig: the stems provide winter interest.
Corydalis
Winter Hazel
Daphne, Winter Variegated
Dutchmen's Breeches
Foxglove
Evergreen Solomon's Seal
Shooting Star
Dragonhead
Alpine Willowherb
these are just a few of the
flowers that will grow in diffent amounts of shade. I also grow miniature snapdragons in partial shade and they don't seem to mind at all. Maybe later I'll list some more for you to look at.