If I'm asked one question about what to plant more than any other, it's this: "What do you recommend for planting in shade?" That's a loaded question, because there's more to consider than just the light level. There's the soil type, whether or not it's dry or wet, and is it truly all shade or does it get some direct sun? And do you want color, foliage or both? Perennials or annuals?
Most people that ask this question have perennials in mind, so that they don't have to plant the area entirely new each season. I always recommend some tried and true shade-blooming annuals for color, such as begonias and impatiens, as well as foliage favorites like coleus and caladiums, but only to round out the framework of the garden area. Since there are likely already trees in place providing the shade, there are several plants that can complement each other at their feet.
Don't overlook Hostas and how versatile they are. They come in sizes from extra-large (Empress Wu) to extra-tiny (Tiny Tears). They're streaked, striped and solid in color, and some have leaves that look quilted. Edges can be rippled or straight. And though they're known for their foliage, many have gorgeous blooms, some scented. They can be planted in the ground or in containers. No wonder they're used so much!
Heucheras are a common choice for shade gardens, too, and in recent years, there have been many new varieties introduced. Again, foliage is the strong point of these perennial performers, although there are some that have brilliant blooms. The leaves come in many colors and patterns - so many that you could highlight a collection of them in your shade garden, just as you could do with Hostas.
Related to the Heuchera is the Tiarella. It has similarly shaped leaves, but the flower plumes are much fuller, as well as being held closer to the foliage. Heuchera and Tiarella have also been crossed to form hybrid Heucherellas, which are lovely in their own right. All of these enjoy the same growing conditions.
One of my favorite shade plants is the toad lily (Tricyrtis sp.). They can have plain, streaked or spotted foliage, and the blooms resemble small orchids. A big advantage of these is that they bloom in the fall, when there isn't much else in flower.
Other shade beauties include violets, cardinal flower (Lobelia sp.), Astilbe, Lady's Mantle (Alchemilla mollis), Brunnera, Epimedium, Helleborus and many ferns. For beautiful texture, try using shade grasses like Carex varieties and Japanese Forest Grass (Hakonechloa), which both come in several shades of green, white and yellow. Some sun-loving plants will also perform well in shade, such as daylilies and creeping phlox.