#1 Knoppix

There is no surprise here, Knoppix is the best linux livecd currently out there, they have been holding this spot for a few years now.
The latest version of Knoppix packs a Linux 2.6.x kernel, KDE 3.x, xmms with mp3 and ogg support, GIMP 2.x and OpenOffice.org

#2 SimplyMEPIS

Based on Ubuntu, SimplyMEPIS comes with a very nice distribution of software and drivers, it has both nVidia and ATI (fglrx) video drivers and madwifi-ng wireless drivers. The default desktop is KDE 3.5.x, with Firefox 2.x. It also has a very nice hard drive installer.

#3 SLAX

The standard edition of SLAX is currently under 200MB, its greatest asset is its modularity, you can customize the system to fit your needs, by adding additional software in the form of compressed modules. It has Kernel 2.6.x, KDE 3.5 and great wireless support (ndiswrapper and madwifi drivers).

#4 PCLinuxOS

Being based on Mandrake, PCLinuxOS offers a great list of software, including a KDE 3.x desktop, instant messaging and irc, NVU for web editing, The GIMP, BitTorrent and Frostwire for filesharing and OpenOffice.org for documents.
A really nice feature I liked about it is PCLinuxOS Control Center, where you can control basically everything (hardware, security, networking and more).

#5 Elive

Elive or Enlightenment live CD differs from the others in that it doesn’t have KDE, instead it relies on the Enlightenment window manager. Its very eye-candy and has relatively low hardware requirements. It has its own control panel called Elpanel, where you can modify desktop and system settings.