Salvia azurea is an underappreciated species native to a wide swath of the middle of the United States. I love it for its masses of true-blue flowers beloved by bees and other pollinators in the fall, and the fact that it is a zone 5 hardy, drought tollerant, tough perennial.
The down side is that unless pruned back early in the season or staked, it flops all over the place.
My seed strain selection 'Blue September' is shorter -- about 4 feet -- with strong stems that don't require staking in my garden. If you irrigate and fertilize heavily your milleage may vary.
As this is a seed strain, there is some variability in size and flower color, including the occational white flowered individual.
You can purchase plants grown from my seed from Select Seeds