Some of the best:
Abelia 'Pinky Bells'. Abelias, once quite dull plants, have come a long way! This is a fairly new plant, with some of the largest flowers on any abelia. In my experience, it starts blooming in the fall, making it most unusual, and it covers itself in bells. Full sun to part shade, it has red new growth. It is a zone 6 plant, so it will need protection in a cold winter, but if you want a plant that blooms from mid-summer to fall, and is deer resistant, this is the plant you want! It has been in garden centers for a couple of years, and can be ordered on line from various sources. The mature size is only about two feet high, and I can attest that it is great in a pot, growing into a beautiful mound.
Clethra alnifolia 'Caleb' Vanilla Spice. This is a newer form of summer sweet, a native shrub, with exceptionally fragrant flowers that are 50% larger than the standard clethra, and it blooms in late summer. Very few shrubs do that. The foliage is deep green, and it is another with gold fall color. This one flourishes in full but also in quite a bit of shade. An excellent all round performer. This is the largest of my recommendations, because while half the size of the species, it is still 3 to 6 feet tall but has the bonus of flowers twice the size of the species, at 10 to 12 inches long. This one does prefer acid soil.
Comanthospace japonica 'Golden Angel' is a non-aggressive Japanese mint relative, sometimes referred to as Japanese Shrub Mint. It jumps out of the shade with golden leaves and white bottlebrush flowers, the latter appearing in summer and fall. Completely winter hardy in zone 5a, I find that it does like moisture, but it really shines in the shade bed, but can take sun as well. It completely lights up the shade garden, and is readily available by mail order. Three feet tall by three feet wide, it is a beautiful companion for hostas or shade loving hydrangeas.
Deutzia gracilis 'Duncan' Chardonnay Pearls. This is a plant from a few years back (it was on Garden Design’s "Way Hot 100" list in 2006, but not often seen in yards despite its east of culture and multiple seasons of interest. It produces tiny buds in April, followed by gorgeous fluffy white flowers in June, and then it displays stunning lime yellow fall color. And size? Here it is under a pink PJM rhododendron. The perfect small plant. The one in the picture is a mature plant. Completely hardy in zone 5a.
You are probably familiar with Fothergilla gardenii, but it’s such a great plant that I must include it. It is a shrub that can take full sun to full shade, although fall color is more vibrant with some sun. The height and width is 2-3 feet, with similar width, and it is a slowly suckering plant with fragrant bottlebrush flowers in spring and dazzling red, orange and yellow color in the fall. I found that the plant responds well to a bit of acidification, but after that requires little to no care.
The PJM rhododendron is a wonderful plant for cold climate growers. Evergreen, it blooms in very early spring with magenta pink flowers. There is one in my yard that is 30 plus years old, and the previous owners did nothing but prune it. Despite the fact that it is commonly believed to be a part shade plant, mine is on the south side of my property, being used as a foundation plant in full sun. Mild acidification and a little water just make the plant more spectacular. The only problem is the size. A height and spread of three to seven feet is too much for many yards, although it is amenable to pruning. But that problem has been solved with the development of ‘Checkmate’ which resembles it but is only three feet in height. Like PJM, it blooms in early spring with magenta pink flowers. It has small leaves that, like its big sister, are an attractive olive green and copper colored in the winter.
Lastly, I must sing the praises of the oakleaf hydrangea. Spring flowers, fall color and exfoliating bark; who could ask for more? And now there are multiple small varieties. I own Hydrangea quercifolia 'Pee Wee' and 'Sykes Dwarf'. The United States National Arboretum, in 2011, introduced 'Ruby Slippers', a cross between 'Snow Queen' and 'Pee Wee'. It is thusly names because the flowers start as a creamy white, turn to pale pink and then deepen to rose. It is three feet high and about five feet wide, with 9 inch upright flowers. Also introduced in that year was ‘Munchkin’, which grows three feet high and four feet wide, with white flowers aging to pink. The only caveat for this plant is that, in zone 5, it should be wrapped in burlap to avoid the loss of the flowers in the spring.
With these shrubs you will have color in your garden from early spring through fall.