http://backuppc.sourceforge.net/ (Recommended by Jim)
http://geekconnection.org/remastersys/ Remastersys is a tool that can be used to do 2 things with an existing Debian, Ubuntu or derivative installation.
It can make a full system backup including personal data to a live cd or dvd that you can use anywhere and install.
It can make a distributable copy you can share with friends. This will not have any of your personal user data in it.