Did you had ever heard about BackTrack? BackTrack is one of the linux distro based on ubuntu which is dedicated to digital forensics and penetration testing use. The latest version of BackTrack is BackTrack 5 R1.
BackTrack provides users with easy access to a comprehensive and large collection of security-related tools ranging from port scanners to password crackers. Support for Live CD and Live USB functionality allows users to boot BackTrack directly from portable media without requiring installation, though permanent installation to hard disk is also an option.
For me, I just installed the GNOME one on my laptop and below is my current desktop. I like this version because in the previous version (Backtrack 4), i got issue whereby i can’t connect to internet via wireless due to hardware problem. Magically in the BackTrack 5 R1, everything works perfectly! (At least for the time being).
If you are new to linux, it is not encourage for you to use this distro. You maybe want to use Ubuntu instead because the Ubuntu is quite same compared to Windows operating system (I mean the user experience). You may use lots of GUI in Ubuntu compared to this distro.