Yikes, Mike. I don't know what it is but unless you really really like it, I'd start cutting off those flower spikes before the plant or the birds spread the seeds around! Those long spikes all have a ton of seeds forming at the bottom.
It's big and lusty and looks like it's ready to try and take over. You could save the seed, and plant it again yourself if you find out what it is and really like it.
Up side is, if you cut off the older flowers it will keep making new ones longer . . . It IS kind of pretty.
