D is for dianthus. At least in my zone (Pennsylvania) this hearty perennial comes back yearly with no attention whatsoever. It gets bigger each year, but only by a bit and it stays bushy without taking over the garden.
Bee Balm Monarda - A favorite with hummingbirds, these brilliant monardas explode forth from tall stems to catch the attention of your garden visitors. Grows to 24'' to 36'' H Perennial Bloom period: summer Full sun to partial shade Hardiness zones: 4-9