Arch Linux
A great Linux distribution for advanced Linux users, very configurable.

Slackware Linux
Well rounded and secure distrubution. Not on the bleeding edge but easy to update and configure.

Gentoo Linux
A great all around Linux distribution where you compile everything.
checkuse.sh - Lists emerged programs compiled with old use flags.

Mandriva Linux
A great desktop Linux distribution (formerly Mandrake).

Ubuntu Linux
A Gnome desktop oriented version of Debian that is free.

Kubuntu Linux
If you like Ubuntu but prefer KDE to Gnome.

Debian Linux
Excellent update/install system in aptget. Use the Debian-Installer.

SuSE Linux
Recently purchased by Novell so its "free" future is uncertain.

Fedora Project
RedHat distribution for testing componets for RHEL.

The Linux Documentation Project
A great resource, HowTos for everything under the sun.

Slashdot
A great news site for computer (and other) geeks.

OS News
News site for people interested in operating systems and related.

CrossOver Office
Runs Windows applications under Linux.

Cedega (WineX)
Runs Windows games under Linux.