Damn Small Linux(DSL)
Damn Small Linux is a very versatile 50MB mini desktop oriented Linux distribution.
Site: http://www.damnsmalllinux.org/
KNOPPIX
KNOPPIX is a bootable Live system on CD or DVD, consisting of a representative collection of GNU/Linux software, automatic hardware detection, and support for many graphics cards, sound cards, SCSI and USB devices and other peripherals.
Site: http://www.knoppix.org/