MaxPainCode develop a new dos tool is based on a new attack that uses HTTP Flood to get the site down, this will work if you try with big dedicated server. Another Feature of Assassin DoS is that it will not take all your resources as the most DoS do. Also its like only 100 mili seconds delay when hitting the target and its available for windows.
Same Issue is Discussed with Microsoft Security Response Center by Developer of This tool.
Its available to Download here (Disclaimer : Use it at your own Risk)