BLDGBLOG has a great post about some innovative skyscraper desgins by a gentleman named Loren Supp. These were apparently done as part of a design competition for eVolo Architecture, and the other finalists and winners, too, are worth a look (the site is Flash, and prevents direct linking, but check out Peristal City, "A Circulatory Habitat Cluster for Manhattan" by Neri Oxman and Mitchell Joachim, if you get a chance).