Kerria Japonica is lovely in the shade and mine was blooming in Aug - Sept. However, it is taller than your 1 - 2 ft tall limit.
Astrantia major (Masterwort) flowers all summer and does well in part shade. It is about 18" tall. It's a lovely delicate flower and comes in colours from ivory to red.
Astilbe chinensis pumila is a late flowering and a long flowering Astilbe but it may be a bit short for you.....up to about a foot tall. It spreads readily when it is established and has pinkish flowers.
Jacob's ladder (Polemonium) also does well in the shade and is in the height you are looking for. Most varieties bloom in late spring but some will re-bloom in late summer if they are dead headed after the first flowering. One that re-blooms for me is 'Heavenly Habit'. There is a variegated leaf type called 'snow and sapphires".
Yellow Waxbells (Kirengeshoma) is hardy to zone 5 or to 4 with protection. It's about 24" tall and flowers in late summer or early fall. It likes moist soil.
Turtlehead (Chelone obliqua) will flower into late summer with deadheading. It grows somewhere around 2 feet in height. It likes moist soil.
Dendranthema rubella or Fall Daisy will flower nicely in shade although it prefers a bit more light.
Toad Lily is hardy to zone 5 possibly zone 4 with protection. It flowers in the fall. 'Lightning Strike' has variegated foliage too.
Hardy Cyclamen bloom in late summer to early fall and are hardy to zone 5. Might be a bit short for what you want.
I'm sure there are more out there too. Good luck.

Gilli has selected some lovely perennials for you Lorraine, but she forgot Cowichan primulas from her part of the world. Hellebores are just coming into flower in my garden.

some penstemons and hemerocallis will also tolerate some shade too. what about ferns ? and hardy geraniums.