There is nothing like free plants, and that's why I am such a fan of verbena bonariensis, that tall, purple-topped spike that self-seeds so abundantly in my garden.
If some pop up where I don't want them, I have no qualms about pulling them out because there will be plenty growing where I do want them. Right now, they are doing what they were designed to do, according to my Dave's Garden newsletter -- create a kind of screen.
I have always butchered the pronounciation of this verbena, and it comes out sounding like the last name of David Boreanaz, the hunk who starred as Angel in "Buffy the Vampire Slayer" and now plays the dumb, strong guy opposite the smart woman in "Bones."
But it is actually pronounced bon-ar-ee-EN-sis and it is named after Buenos Aires, the capital of Argentina, a reference to its native habitat, according the Dave.
I actually use it as a backdrop for smaller plants. But to each, his own.
A word of warning: It is vulnerable to powdery mildew.
PS Dave's Garden is an excellent source of plant information and gardening reviews, as well as insect and bird info. Visit the site and sign up for his newsletter, if you haven't already.