I love that Lily of the Nile, I was going to suggest that but the one I googled said it was only hardy to zone 8, but park says 6?
Julia, I wasn't sure if you were looking for something clumping or blue. The Stella de Oro is clumping and the Caryopteris is blue.
How about some Siberian Iris, good to zone 3
http://urbanext.illinois.edu/p...