I know hostas and huecheras bloom, but I think they're grown more for the foliage. Maybe astilbe? If he needs more of a ground cover than a shrub, then maybe sweet woodruff or vinca would be an option. I'm having to find stuff for full or part shade here at our new house, too, but I haven't been looking so much for flowering plants.

dI think a lot will depend on how deep the shade is because some shady areas are dappled and some plants will bloom in the dappled shade and some shady areas have a fairly good amount of light even if it often is just being reflected off adjacents walls or fences.

In addition to the plants miraje mentioned, I think hellebores would work well in shade, and some of the ephemeral woodland plants like Virginia bluebells and other early-season bulbs probably would perform there. Spiderwort ought to bloom even in shade. In our woodland we have the brief appearance of jack-in-the-pulpit in spring, and woodland violets and woodland phlox as well as some of the native ruellias. We have four o'clocks blooming in the dappled shade beneath a large pecan tree, but they do get a little direct sun early in the day. They get taller in shade, but they still bloom well. Most of the native woodland plants that we have will bloom only for a few days to a few weeks, so you don't get the same effect that you get from shade-loving annuals like begonias or New Guinea impatiens that bloom for months at a time. One of our prettiest understory plants in our woodland is American Beautybush. It forms a deciduous, arching shrub and the actual flowers are not impressive, but the violet-colored berries provide lovely color for several months. We also have Gregg's Mist wildflowers growing and blooming in dappled shade in the woods, so they might work for your friend. While they are not perennial, caladiums can provide a lot of color, and I have the large green-leaved alocasias growing in morning sun and dappled shade. They don't bloom but they do come back every year and are a dramatic and striking presence underneath the trees.