Here is a nice little ddos script which works well.
Installation
wget http://www.inetbase.com/scripts/ddos/install.sh
sh install.sh
Uninstalling
wget http://www.inetbase.com/scripts/ddos/uninstall.ddos
sh uninstall.ddos
Their site is currently under construction but the script is accessable http://www.inetbase.com/scripts/ddos/
Remember, make sure you do not leave this script running on the server. When the ddos is over, turn it off!
