Debian GNU/Linux: Official site. One of the most important distributions, uses only Free Software as defined by FSF. Descriptions (Social Contract, partners, donations), news, sources, packages, documents, support, developer corner

Debian Reference: Manual for experienced users wishing to learn more about Debian. In HTML, plain text, PS, PDF; English, Deutsch, Español, Português, Français, Italiano; short and full length versions

DistroWatch: Compares Linux distributions (major, minor, regional) in simple table format. Information such as price, support, documentation, included packages

Fedora Project: A Linux based operating system. Download, documentation, FAQ, and wiki. Official site

Gentoo: The official pages for the distribution provide documentation, downloads and installation instructions, mailing-lists, forums, performance reviews and news

Knoppix: The official site, with information, links to download sites and CD vendors

Red Hat, Inc.: Official site; news, support, documentation, whitepapers, downloads, consulting, training, embedded solutions

SUSE Linux Enterprise: Novell-owned Germany-based distribution. Find official news releases, links, and corporate information

The Slackware Linux Project: The original Linux distribution, geared towards power and stability. FAQ, support, news, mailing lists, downloads, and links

Turbolinux, Inc.: Distribution, products, and services for large scale, to small scale and web businesses. Strong in Asia Pacific region, largest Asian distribution, founded 1992. Sites in English, Chinese, Japanese

Ubuntu Linux: Official site; Commercially sponsored Debian-derived Linux distribution that focuses on usability, a regular 6-month release cycle, and a commitment to at least 18 months of security updates for every release