http://www.thermalright.com/a_page/main_product_hr01_775.htm, but they now have 'plus' and 'X' versions too. The duct goes over the cooler and the rear 120mm fan so all the air from the case goes through the cooler and out. It's an excellent and very simple idea that works really well now the chipset cooling is sorted out with the P35 chipsets.
http://www.thermalright.com/a_page/main_support_installation_fanduct_hr01.htm shows it at work.
http://www.thermalright.com/a_page/main_support_installation_fanduct_hr01.htm shows it at work.