BackTrack
Well this is not a tool. This is THE Tool set, the only thing you will ever need during a penetration test (you dirty minds, you thought *that* penetration? nooo it’s just a security penetration, sorry).
I am using this distro all the time, and it continues to surprise me with new and new possibilities. If you decide to give it a try, don’t forget to FIRST check the forums, the wiki, or our IRC channel at freenode – #remote-exploit. I will never forget a new user, asking in the channel “Is this the BlackTrack support channel?” – and the reply – “This is not the african detective agency support channel, no” 
so… just listen for a while, before starting asking questions there, please. It’s for your own good.
I will be using this distro for a lot of the posts in the blog, so make sure you have it ready on a CD, DVD, or USB drive. I personally prefer the USB drive with changes (more on that on the forums) – if you mess up, delete the changes folder, and your USB live distro is virgin again! Don’t you wish it was that easy in real life, huh?