BackTrack3

This is a VERY useful Linux Slax live CD developed for Penetration Testing. All you need to do is burn the .iso image to a CD and boot to it after a restart on any computer. BT3 has a NICE collection of tools that can be used for hacking, windows password cracking,network mapping, and a bunch of other fun tools to mess around with. It also has KDE and Flux, so it has a very friendly GUI. Check it out!