When it comes to hacking, security, forensics thing like that, linux is the only and the preferred tool. Linux is very hacker friendly from ground up. But still there are distros that are more oriented towards assisting hackers. To name a few, backtrack, backbox, blackbuntu etc.
Backtrack is the most popular distro when it comes to penetration testing and security stuff. And now it has taken a new avatar called Kali Linux. Kali Linux is the new name of backtrack (version 5 rc3 was the last backtrack release).