Seiichiros HP with useful stuff about GNU/Linux, bash, Nokia Nxx0 and more.
Eanderalx' HP with useful stuff about GNU/Linux, bash, perl and more.
Linux Beginner Guide
Advanced Bash-Scripting Guide
VIM Tips and gVIM key features
Sed - An Introduction and Tutorial
LaTeX-Befehlsreferenz: Übersicht
Regular expression tester and guide
Helpful tutorials for many stuff (I used the tutorials about Virtualbox)
Why we use Linux
Linux Games For Non-Gamers?