Baptisia australis
This large, hardy perennial (also called 'false indigo') is available in blue or white. The blue is the truest blue in my garden. It makes a sturdy clump as wide as it is tall and stays there for years. It likes moist, humusy soil (lime-free), and will grow in full sun to partial shade, blooming in June. The seed pods and flower stems turn black after the flowers are spent. I think they are quite ugly, but I keep reading that most people think they are "interesting for dried arrangements."
It self-seeds all over my yard, and I let it stay where ever it appears. It's my absolute favorite background plant because it is pest free, sturdy, and has lovely glaucous foliage even after the pea-like flowers fade.
Both blue and white baptisia with salvia in front and weigela in bloom behind.
Baptisia in bloom in June.
The white baptisia is elegant in bloom. Shown here with the Cornus kousa also in bloom to the left and the red Japanese maple in its glory.