I would suggest Anemones for spring and/or fall blooming and bergenia or lungwort, Astilbes & coral bells for summer, ligularia and lobelia for late summer, Japense Painted ferns which stay nice and tidy. Any type of hosta. You could also plant in the way of shrubs hydrangea or sweetspire as they like the shade. Ground cover like bishops weed or ajuga or lamiastrum (herman's pride) like shade. Spring is the easiest time to plant new perennials don't fertilize just give them root stimulator for the first season. Don't plant them in rock use mulch, as even in shade the roots can get too hot.