Brainz.org has a very good article which gives 15 excellent examples of designs inspired by nature (biomimicry or biomimetics).

Are you smarter than a goose? Sure you are -- one on one. But when it comes to working efficiently, you and your colleagues can't touch the gaggle. According to author Ken Thompson, geese and other animals that naturally form groups have a lot to teach us about business. In a theory he calls organizational biomimetics, Thompson lays out the principles underlying nature's management strategies. So what can you learn from a bird or an ant? Take a gander. Katharine Gammon at Wired Magazine reports.