This excellent website allows you to create a floppy disk, USB stick or CD-ROM which you can boot any computer from. It connects to the Internet and downloads a list of operating systems which you can install/boot. This is great because you don't always know which operating system you might need. One day you need Ubuntu, the next you might need Linux Mint. The site also gives you the opportunity to customise it so you can boot a system which is not on the large list of systems preconfigured to boot.
Here is a video of the system in action, check out this great site at www.netboot.me.