SystemRescueCD can go on both a CD and a USB stick. When your Linux or Windows system goes haywire boot it up and commence rescue operations. All the best rescue tools for Windows are in Linux. It's also a great tool for preparing a system for a new operating system installation.

SystemRescueCD supports a large number of filesystems, has a modern linux-2.6.29 kernel, and the new Xorg-server-1.5.3. You can work from the console, or boot to the XFCE desktop, which is lightweight, sleek, and very easy to learn your way around it. It includes networking, partitioning, cloning, LVM, and RAID, and you even get a nice utility for making your own customized SystemRescueCD that includes any extra applications you want.

The documentation is pretty good, and here are some articles that tell some ways to use SystemRescueCD.

Become A System Rescue Guru With Linux, Part 1
Become A System Rescue Guru With Linux, Part 2
Partition and Image Your Hard Drive with the System Rescue CD
Change Your Forgotten Windows Password with the Linux System Rescue CD