Ubuntu on your usb stick

You can now install and/or run Ubuntu OS from a USB flash drive, which allows users to run the Live CD experience without the need for a CD.

Ubuntu Tips & Tricks shows you how to install Ubuntu Linux on a flash drive, thus giving you the Live CD experience without the CD.
You’ll need a system that’s already running Linux. You’ll also need a 1GB-or-larger flash drive, a Live CD and some familiarity with the Linux command line. The tutorial looks pretty straightforward, though it’s definitely not a five-minute project–and not for novices, either. If you’re looking for an easier method to boot Linux from a flash drive, try this option, which employs Knoppix and works from Windows. However you go about it, there’s no question that bootable-Linux is much cooler on a flash drive than it is on a CD.