One important attribute of flowers is texture. The texture of the foliage, of course, but also of the flowers themselves contributes to the overall ambience of a garden.
One of my neighbors has a row of hydrangea (paniculata grandiflora), in his front yard, and the bushes in late summer are covered with rosy colored, flowered panicles with breath-taking texture. They seem crinkly and wavy at the same time, and I love looking at them.
Crepe myrtles have a similar crinkly looking flower but with less substance so they have a more delicate texture. During early summer I almost swooned when I saw the first bloom on my Louisiana iris ‘Black Gamecock'; its purple-black velvety texture is just impossible to describe. It looks luxurious but is as tough as nails, tolerating heat, cold and humidity.
The flower spikes of lavender are also wonderfully textured, as are the lupine-like spikes of baptisia flowers. And consider the bristly texture of globe thistle flower balls that are reminiscent of medieval maces. Clematis ‘Crystal Fountain', and indeed many clematis flowers with defined stamens, also have lovely texture.