The Linux documentation project: all docs, manpages, HOWTOs, FAQs

Google for Linux: the specialized search engine

Deja: an archive of all newsgroup postings, including the comp.os.linux hierarchy

Slashdot: daily news

http://www.oreilly.com: books on Linux System and Network administration, Perl, Java, ...

POSIX: the standard

Linux HQ: Maintains a complete database of source, patches and documentation for various versions of the Linux kernel.

Linux PPC: Linux on a Power PC (e.g. Apple PowerPC, PowerMac, Amiga, IBM ThinkPad/PowerSeries/RS/6000, Motorola...)

AlphaLinux: Linux on Alpha architecture (e.g. Digital Workstation)

Linux-MIPS: Linux on MIPS (e.g. SGI Indy)

Laptop HOWTO: Specific guidelines for installing and running Linux on laptops, configuration files for various models.

MkLinux: Linux on Apple

The Fedora Project: RedHat-sponsored community effort OS.

Mandrake

Debian

TurboLinux

Slackware

SuSE

LinuxISO.org: CD images for all distributions.

Knoppix: distribution that runs from a CD, you don't need to install anything for this one.

DistroWatch.com: find a Linux that goes with your style.

...

Freshmeat: new software, software archives

OpenSSH: Secure SHell site

OpenOffice: MS compatible Office Suite

KDE: K Desktop site

GNU: GNU and GNU software

Gnome: The official Gnome site

Ximian: Ximian Gnome, Red Carpet package management system for StarOffice, Opera, CodeWeavers, Loki Demos, Evolution, system packages, ...

RPM Find: all RPM packages

Samba: MS Windows file and print services

Home of the OpenLDAP Project: OpenLDAP server/clients/utilities, FAQ and other documentation.

Sendmail Homepage: A thorough technical discussion of Sendmail features, includes configuration examples.

Netfilter: contains assorted information about iptables: HOWTO, FAQ, guides, ...

Official GIMP website: All information about the GNU Image Manipulation Program.

SourceForge.net: Open SOurce software development site.

vIm homepage