Parted Magic - The Ultimate Linux Tool
A sysadmin's toolbox doesn't contain physical spanners or screwdrivers, it does however contain tools. We pick them up over the years. Open source software which provides servers, tools, scripts they all end up in the metaphorical toolbox.
One such tool in my toolbox is a Linux distro i found a few years ago and has become invaluable. So much so that slowly but surely converts to the Microsoft cause i work with who felt that Linux offered them nothing are now using this as well.