Plume poppy (with allium)
Echoing Steve, I love the leaves with their cut edges. My main patch is across the living room from my desk, where that foliage is framed in a window and helps block the busy road out front.
On the north side of the house, it's maybe not as aggressive as it might be in a spot with better sun and soil. I pluck a few stray runners early in the season to keep it in bounds. It's not the rampant hog some told me it would be when I first planted it. (I like a plant that can hold its own.) But the plumes do rise up about 7 feet.
I've got a real hell strip about 2 feet wide between the driveway and house with the worst soil on the place where it tops off at about 4 feet. It has a totally different character there.
If anyone wants a start, stop by.