In first year university we had do design a cardboard bookshelf that was to be judged, not only on aesthetics, but by how much weight it could hold compared to the amount of cardboard used. As a result, I have developed an ongoing fascination with furniture make out of cardboard.
Swiss architect Nicola Enrico Staubli has designed a line of furniture based on folding cardboard. What is interesting about his approach is that he is not selling the furniture; in fact he is not actually selling anything. His designs are meant to be constructed by you (yes you). Printable templates are downloadable from his Foldschool website. Nicola says the thinking behind foldschool is "To restore design to one of its original missions: to provide a product at an affordable price through a smart manufacturing process" and presumably by smart manufacturing in this case he means elbow grease. (Thanks Ostrowski!)