Bootable Linux Demo Distro - Knoppix
I am using the "Superrescue" Distribution which is also a CD-Distri in my company when I need to start up another Linux workstation, so I do not need to delete those wondonze stuff nor do I need to install a complete Linux on a computer I am using only once a month. The distri is a little slow in the first boot-up but it also brings Gnome and KDE with most programs. And when that's not enough you can just use it for a "diskless" workstation.
I found the "Superrescue" here: http://www.kernel.org/pub/dist/superrescue/v2/