The 2010 winner is false indigo (baptisia australis), a native North American plant with grey-green foliage, and lovely dark blue pea-like flowers over a long period in spring, followed by attractive black seed pods that rustle in the wind. Around 100 cm (40”) tall with a similar spread, it’s a well behaved addition to your perennial border.
It likes full sun to part shade and average, well drained soil. You can plant it on its own or with spring bulbs. Hardy as low as zone 3; slow to get established, but very long-lived.