I second the butterfly bush one. I only wanted one, and one that will stay at 4-5 feet. Of course it did neither - new plants spring up here and there, and the only one that I wanted requires a major pruning every year. It grows so darn fast.
And Japanese anenomes. I am willing to keep some since they provide great fall color, but boy, do they spread! I have at least two major weeding events pulling out as many as I can, and leave just enough to supply blooms.
