Popular Linux distributions:-
..:   Red Hat    Enterprise level Linux Server from Red Hat.
..:   SuSe    Enterprise level Linux Server from Novell.
..:   CentOS    No-cost rebuild of Red Hat Enterprise.
..:   Fedora    Red Hats no-cost community offering.
..:   Debian    Pure Linux built from and GNU.
..:   Ubuntu    A reworked Debian, emphasising end user friendliness.
..:   Mint    A reworked Ubuntu, even smoother. New users start here.
..:   Slackware    The longest established distro - now over 20 years since the first release.

..:   DistroWatch    More information about the various Linux flavours..

Linux support and documentation:-
..:   Linux system tuning    Improving server performance.
..:   The Linux Documentation Project    The central repository of Linux FAQs and HOWTOs.
..:   Linux User Groups (LUGS)    Find your LUG here for local support.
..:   Linux from Scratch    How to build your own custom Linux system.

A few Linux applications:-
..:   Webmin    A network-enabled configuration toolset for Unix and Linux systems.
..:   The Apache Software Foundation    The world's most popular web server - and much more.
..:   Sendmail SMTP server    An extremely configurable email server software.
..:   Netfilter/iptables    The Linux firewalling subsystem.
..:   The FreeS/WAN project    Build Virtual Private Networks with Linux for no cost.
..:   Open Office    A free alternative to Microsoft Office (also runs on Windows).
..:   SAMBA - opening windows to a wider world    Network filesharing between Linux and Windows.
..:   The Gimp    Photoshop-like graphics package - used for graphic production on Skywhale.NET.
..:   The Mplayer project    A movie player for Linux (beats Windows Media Player in my experience).
..:   Linux Quake    The famous first-person shooting game - developed under Linux, apparently.

More Linux links to follow later.......