Whether it's in a border, as a screening plant or the focus in a backdrop, Persicaria Polymorpha(fleeceflower) will not dissapoint. This plant commands attention, and where I have it in a narrow border, you cannot help saluting it.
It is hardy down to zone three, grows five to seven feet tall and once established does not require much water. It blooms all summer and has fall and winter interest. Mine grows about seven feet tall, and I shared some divisions with my sister-in-law that she uses as a screen. I am going to divide mine this spring (which I haven't done for six years) in order to keep it out of the walkway.
Phlomis Tuberosa (jerusalem sage), grows to five feet, hardy to zone 5, is the lavendar-pink flower in front of the Persicaria. It is a lovely tall plant, but you will need to consider placement (I since have moved it). It flowers for a short period of time, so it is better placed with perennials that will take over for it when it's done
Helianthus Lemon Queen is a stunner in the late summer and fall garden. It can grow to seven feet tall, but after the first couple of years and having to tie it because it is along a narrow strip, I pinch it back in May. It then stays a more manageable height for my location. All of these are available at http://www.diggingdog.com/
Although, I noticed that they do not have "polymorpha" listed at this time - many other varieties.