Here's a perennial that I've simply grown to love over the last few years. Earlier, it had always been somewhat of an oddity, but upon planting one in an older trial garden we had years ago, and in my own garden since then, it has been reliable and impressive.
I'm speaking of Baptisia australis, or the False Blue Indigo, native of Northern Virginia to Western Pennsylvania, east to Missouri and Kansas and south to Georgia and Texas (although the USDA seems to indicate a much wider range, which see here).
Small plants planted in your garden will, within a couple of years, produce large, almost shrub-like plants, 90cm wide by 120cm tall (3' by 4'), covered with Lupine-like spikes of brilliant, indigo-blue flowers in late spring and early summer.
According to Allan Armitage, in his ever-so-useful treatise on herbaceous perennials, the flowers were once used as a subsitute for the true indigo, Indigofera of the West Indies. When the real thing was in short supply, the English government contracted farmers in Georgia and South Carolina in the mid 1700's to "farm" the lovely False Blue Indigo, or Baptisia australis, to produce more dye.
In any case, it's a beautiful and easy plant. I find it self-seeds, but isn't a problem. The seedheads in late summer make interesting "rattles" for young children, and likely useful as ornaments in dried flower arrangements.
Also of particular interest in recent years, is the renewed effort in Baptisia selection and breeding. One I am quite excited about is Baptisia TWILITE PRAIRIEBLUES, an interesting hybrid between B. autstralis × B. sphaerocarpa.
A cool article on the genus by plantsman Tony Avent is available here. He refers to them as the Redneck Lupine, and for all intensts and purposes, Baptisia is indeed a much better choice for the usual summer heat and humidity experienced throughout most of North America.