I have Actaea simplex 'Brunette' which is a beautiful plant. That's tall. There are also some geraniums that will grow in shade. G. nodusom, G. macrorrhizum, G. sylvaticum and G. maculatum. The last two are about 15" tall. Look at G. mac. 'Beth Chatto' - she's lovely! So is G. syl. 'Amy Doncaster'. Another medium-sized plant is Lamium orvala. I posted a photo of it on my page, so you can take a look. Brunneras - plenty of those to choose from. Cardamines are lovely for the spring - as long as you mark where they are as they disappear in the summer. Pulmonarias - lovely all year round with silver leaved varieties; flowers in early- mid spring.

Small plants - Omphalodes cappadocica can't be beaten. 'Cherry Ingram' has the biggest flowers. There are also lots of little pretty Anemone nemorosa.

have a look at the plants in my profile, if they have a tag shed border, under beech tree, or side drive then they are all shade tolerant or shade lovers.
hope this helps.

Epimediums are good and flower in spring. Some disappear and others keep their leaves all winter. I discovered Erythroniums last year - 'Pagoda' is doing well. Japanese anemones flower in late summer and tolerate shade beautifully.

Pulmonarias (shades from pale pink to deep blue, some with spotted leaves and some plain - but tend to get mildewed if the soil is very dry) dicentras, Solomon's Seal (sorry Bamboo, can't remember its Latin name!) & fibrous rooted bedding begonias for summer. For spring bulbs, daffodils, snowdrops and anemone blanda.