A Frenchman is making "green walls". Which are exactly what they sound like. Rather than a wall being made of wood or concrete, he's making them out of living plants. Well, the wood and concrete are still there, you just can't see them any more because the wall is entirely covered with plants. Think dense jungle on the side of your office building. Or in the lobby. Check out his site, Vertical Garden, because the pictures are cool and the final products are currently stumping my powers of description.
These walls are probably too "designer" for practical, wide-spread application. Watering and fertilizing are done automatically, and some walls need artificial light. Heaven help you if the power goes out. I'd like to see someone take the green wall concept and modify it so that it has more structural support and requires less coddling. While they are still rare, green roofs are starting to show up on more and more buildings; how cool would it be if some of those buildings also had green walls?
Maybe I'm crazy, but what I'd like to see someday is green cities. The city would still be home to lots of people, and there'd still be roads and transit. But the "green spaces" wouldn't just be sidewalk trees and parks. The roofs would be green, the walls would be green. People would share habitat with more wild creatures then you currently see in a city. We could have both our high-tech world and our natural world, side by side. And with all that green, maybe we could do something positive for our planet instead of just stripping it barren.