This 12-story, 350,000-square-foot building in Cambridge, Mass., that houses biotechnology company Genzyme (recently acquired by Sanofi-Aventis) snagged LEED Platinum status very early on -- back in September 2005. At that time, it was the largest corporate office building to hold the rating. The glass exterior and central atrium allow for oodles of daylight, while heliostat mirrors track the sun and direct even more daylight into the interior spaces. The plumbing reduces water consumption by 34 percent compared with a "typical" building, while energy costs are estimated at 42 percent less. (Photo by Anton Grassi)