Damn Vulnerable Linux is another interesting platform for pen testing and vulnerability assessment, it is created for training purposes to IT-Security professional during a university lessons by the IITAC (International Institute for Training, Assessment, and Certification) and secure software Engineering in cooperation with the French Reverse Engineering Team.
It is freely available for download here:
Damn Vulnerable Linux
And you can find more about it in the official site.
Damn Vulnerable Linux (DVL) is for educational purposes only!