Here are the links to the official sites of Linux distributions.

The Debian Project
The Debian Project is an association of individuals who have made common cause to create a free operating system. This operating system that we have created is called Debian GNU/Linux, or simply Debian for short. Debian, the producers of the Debian GNU/Linux system, have created the Debian Social Contract. The Debian Free Software Guidelines (DFSG) part of the contract, initially designed as a set of commitments that we agree to abide by, has been adopted by the free software community as the basis of the Open Source Definition.

Suse
Your PC has more to offer than the market-leading operating system reveals - more stability, more reliability, and more variety. In several editions for various user groups and needs, SUSE LINUX provides more than a mere alternative to the Windows family. With an installation routine that even newcomers can easily master, and with all advantages of the Open Source world.

Knoppix
KNOPPIX is a bootable CD with a collection of GNU/Linux software, automatic hardware detection, and support for many graphics cards, sound cards, SCSI and USB devices and other peripherals. KNOPPIX can be used as a Linux demo, educational CD, rescue system, or adapted and used as a platform for commercial software product demos. It is not necessary to install anything on a hard disk. Due to on-the-fly decompression, the CD can have up to 2 GB of executable software installed on it.

Slackware
This site is dedicated to providing the latest news about the Slackware Linux distribution, as well as installation help, configuration help, and other general information about Slackware Linux.

Mandrakelinux
Mandrakelinux is a friendly Linux Operating System which specializes in ease-of-use for both servers and the home/office. It is freely available in many languages throughout the world.

Mepis
Mepis is a nice single disk distribution of Linux. It can be run from the CDROM and then installed easily from there. It is based on Debian.

Kanotix
Kanotix is a rock-solid Linux based on Debian-Sid, which contains the newest packages and recognizes more modern hardware than any other operating system in use today. Kanotix is assembled for 32 Bit i586 and for AMD 64 using the most up-to-date kernel with unique patches. Kanotix will run as a LIVE-CD on practically any computer – automatically detecting and configuring virtually any piece of hardware. It is ideal for analysis, data rescue, forensic work, removal of viruses on Win-PCs - or simply for safe surfing and mailing in an internet cafe. It installs to your hard drive in just a few minutes and is ideal for use on your desktop workstation or notebook, or as a server. Quote from www.kanotix.com.