Living walls, walls with special fixtures that allow you to plant vertically, are becoming increasingly popular. They can be difficult to maintain because they're hard to water and the plant's roots don't have very much room to develop, but I've seen some that were very impressive. This is a display at the Philadelphia International Flower Show that makes use of a lot of tropical plants. Generally I've seen them done with either creeping plants or some type of succulent, like sedum. Plants that are drought tolerant seem to work out best.