A repository of nearly 100k RPM packages for various Redhat derivative Linux distributions, such as Redhat Enterprise Linux, CentOS, and Fedora Core.
A daemon that implements granular auditing and logging of OS-level events on Linux systems. Requires kernel v2.6.0 or later.
Your one-stop RPM repository for all the packages that Redhat and Fedora Core won't package, like basic MP3 playback support.
An excellent tutorial on hardening CenOS Linux (and by extension Redhat Advanced Server).
A couple of YUM tricks for Redhat derivatives which will no doubt come in handy for sysadmins.. such as removing all X related packages in one fell swoop.
What to do if you need to add a module to the initrd on a Redhat system (say, you enabled AHCI support on a SATA mainboard and the kernel freaks out).
How to activate the RAID on a Redhat system you've booted from a rescue disk and chroot into it to fix things.
What to do when you see the dreaded "Call to undefined function filter_var()" error message in your Apache logs. It's actually easier that it sounds but I recommend matching the version of the PHP source you download to that installed from your distro's official package.
How to configure password complexity on Redhat Linux machines (and its derivatives). After playing with it for a while, I'd call this a best practice because it requires all of the different character classes but doesn't give you bonus points for using any one (i.e., you have to use them all, but they could the same insofar as character scoring is concerned).