I don't think I've ever seen another plant with this much personality.
The old man cactus (cephalocereus senilis) is one of the funniest things I've ever seen. It looks like a regular cactus; however it's covered by more long white hair than needles. In fact, the smaller ones look something like a furry pickle. When it reaches maturity, it produces rose colored flowers, and bears fruit. It's native to the Hidalgo-Guanajuato region of Mexico, where the hair protects it from the heat and sun. It lives a long time, and can grow to be 45 feet tall.
If you want to keep one in your house (or, in some places, near it as landscaping), it's fairly easy to take care of. You don't have to water it very often, and (as long as it doesn't get too cold) it will live a long, woolly life. Should you find its hair too dirty, you can wash it with diluted shampoo. To keep it small, trim off the top every spring, dry it for three days, and then replant.