You're probably thinking, 'Ah yes, stinging nettle. It'll go nicely next to my poison ivy and poison oak.' But really, stinging nettle is a pretty neat plant. Aside from being a host plant for butterfly larva, it is edible and purportedly has a range of medicinal properties. The stinging hairs that irritate the skin upon contact are removed by boiling, and then you can make it into tea, soup, pesto, whatever. As always, do your homework before consuming any wild plant.
Stinging nettle is a tall, rhizomatous species that will spread along areas with plenty of moisture. It's a good choice if you have a ditch or other wet area where people don't venture too regularly. Use gloves when handling.
Plant with other streamside inhabitants such as nettle-leaf giant hyssop, western coneflower, large-leaf avens, wild mint, and cutleaf coneflower.
Photo credit: Frank Vincentz, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons
Urtica dioica ssp. gracilis