Most of these are gentoo specific, but some aren't. They should work in all distributions, given a few changes due to package managers.

Most of these also come straight from the gentoo documentation, but I have seperated it out in seperate links. Some links are to forum posts that have helped me. Some are links to the gentoo-wiki. All of the links will help you in your quest for mastering Gentoo. I will add links here as I find them and add them to my favorites.

Mods, you may move this where necessary, but I figured it would be best suited in Gentoo because of the Gentoo specific nature of a lot of the links. I just figured I would share the links that help me most, and I happen to stumble upon while surfing.

Administration
Sudo'ers guide

LAMP
PHPMYADMIN

Desktop
XGL
AIGLX
Compiz on XGL
Using different window managers on KDE
Direct Rendering on Intel Extreme Graphics
Gensplash
Extra Buttons on Mice
Mouse Scrollwheel
More Mouse Buttons Help
Automounting In KDE
XGL and Compiz General Tips for Gnome and Nvidia
Compiz via Gentoo Wiki
New Freetype subpixel font rendering

Emulation
Qemu How-To

Hardware
ATI Drivers
More ATI Driver Config
DRI How-To

Kernel
Kernel Flavors
Kernel Configuration Guide

Laptop
Synaptics Touch Pad
ALPS/Synaptics Touchpad

Mobile Phone
Motorola Phone Programs

Multimedia
Command line switches for LAME
Mplayer Plug-In
PkLaunch for Yahoo Music in Mozilla

Network and Sharing
Samba
Email System for a Home Network

Peripherals
Digicam USB Permissions

Portage (and Compiling in General)
Ccache
Bash By Example
Distcc
Gentoo Overlays

Remote Access
XDMCP How-To

Wireless
Wireless Configuration and Setup