Hostas, while noted mostly for their foliage, also generate purple flowers. Cultivars such as Spritzer grow to 18 inches, but the flowers emerge on long stems (scapes) as tall as 30 inches. The purple flowers open during July and August. Another hosta cultivar with purple flowers is Christmas Candy, a variegated form with white-centered leaves. It grows rapidly and, like most hostas, tolerates urban pollution. Other possibilities for your shady sites include hosta cultivars Stiletto, Temple Bells and Sugar Plum Fairy.
The hellebores and their hybrid forms generate purple perennial flowers in the shade. One hybrid form called Blue Lady possesses bluish-purple flowers, blooming in March through May from USDA hardiness zones 4 through 9. Other hellebores that thrive even in full shade include the Red Mountain hybrid. It has rose purple flowers, grows to 18 inches, and works as a ground cover or in shady parts of a patio. The Ballard's group of hybrid hellebores contains some known for their purple flowers; hellebores also go by the name of Lenten roses, for their early blooming times.
The toad lily looks as if a careless painter spilled purple all over a white flower. This species of lily blooms in shady, damp areas, growing to 24 inches tall and flowering in August. Samurai, Gates of Heaven and Gilt's Edge are purple cultivars of toad lily. The wood lily's shade of purple has a brown component to it. These perennials do well in shade, but those found in the wild do not transplant well.
The wishbone flower is a purple annual that tolerates shade. Mrs. Henry Schroeder is an evergreen azalea adapted to the shade and capable of turning out a pink-purple flower in May. Lavender and purple are among the colors of gloxinia, a tropical plant from Brazil. Growing from bulbs, it survives in the shade from zones 11 through 12 but is suitable as a houseplant that you can bring outside in the summer. Disanthus is a deciduous shrub, able to withstand full shade and producing small purple flowers very late in the growing season -- during October.