Live CDs - a way to choose your distro
A Live CD allows you to test-drive the usually latest stable version of KDE SC without the need to install Linux or to change your existing Linux installation. These distributions boot and run completely from the CD and don't modify your hard disks. They can therefore be tried on a Windows computer without risk. All listed CDs are freely available for download.
Kubuntu LiveCD
A live CD version of Kubuntu Linux, Ubuntu's KDE Plasma Desktop option. Kubuntu also offers the Kubuntu Active Technology Preview, a preview of Kubuntu using the Plasma Active tablet experience.
openSUSE Live-CD
openSuse is a stable, yet reasonably up to date distribution..
Fedora
A fast paced distro targeting users who want the latest and greatest available in the world of FOSS. Fedora KDE usually has the latest stable version of KDE in the repositories, and beta versions are usually shipped via supported extra repositories.
Linux Mint
Linux Mint is based on Ubuntu and Debian and is aimed at beginners. There are versions of Linux Mint for several desktop environments. Be sure to get the KDE version of the Linux Mint Live CD.
Chakra
The Chakra Project is a promising newcommer. Originally based on Arch Linux, Chakra is focused solely on KDE workspaces. It is possible to install third party applications, as well.
Mageia
Mageia is a community based distribution. It is a fork of Mandriva.
Netrunner
Netrunner is based on Kubuntu with it main focus on KDE, and aims to be complete operating system for both beginners and experts.
Tanglu
A Debian-based distribution with an emphasis on the desktop and good KDE integration.
KaOS
KaOS is a "rolling release" distribution focused on KDE.
Sabayon
Sabayon is a "rolling release" distribution, meaning that you install once and have your system upgraded as new versions of installed software is added to the distribution. Perhaps not the easiest distribution for users new to Linux.
Korora
Korora aims to be easy for new users, but still useful for experts. It is a community project based on Fedora.
Mepis
Based on Debian, Kudzu by Red Hat. The disk also offers installation to hard drive.
PCLinuxOS
Based on Mandrake (now known as Mandriva).
SuperX
An Indian project, SuperX is based on Ubuntu. From the project site: SuperX uses a tweaked version of KDE and is aimed towards beginners, casual users and business looking for a well supported user-friendly Linux OS.
ROSA
ROSA, a Russian company, offers their enterprise solution ROSA Marathon 2012 for download. The new ROSA Desktop.Fresh edition is aimed at regular desktop users.
Slax - Live CD
Based on Slackware. With modular structure and pseudo read-write CD filesystem. Slax can be run from a USB Flash Drive. Slax has no graphical installer; if you want to install Slax on your machine, you must follow the simple instructions in the Introduction document.
Aptosid - successor to Sidux
Aptosid is an operating system based on the Linux kernel, Debian's branch (called "Sid") and many free and open source applications.
KXStudio
KXStudio has a focus on audio and video production. Currently, it is based on Ubuntu and has KDE as its officially supported desktop.
Pisi Linux
Pisi Linux is another project building on the original Pardus project. Pisi Linux is a community project and supports many languages.
OpenMandriva Lx
OpenMandriva Lx aims to be easy to get started with but also cater to the advanced user. OpenMandriva is a community project.
Kwheezy
From the project site: Not so much a distribution based on Debian, but rather "a well configured Debian KDE installer". It is designed to give you more out-of-the-box. To be easier for Linux or Debian newcomers.
Porteus
Designed to run from a USB flash drive, Porteus is small and fast. Porteus is a community project based on Slackware.
Bridge Linux
Based on Arch Linux. The installation and setup procedure is not as simple for new users as most live systems.
Neptune
Another KDE-only distribution based on Debian.
New Live CDs and DVDs are becoming available all the time. If you've heard of a distro and think you'd like to try it, do an Internet search for it. You may well find that a Live CD is available.