Here's a log of some things I've learned to do in Linux (mostly here so I don't forget)
OpenSSH - The open secure shell
OpenVPN - OpenVPN
Encryption - Various Encryption tips
Eye Candy - Various look and feel issues
Removable Storage - Various tips about removable storage
FreeNX - Fast and secure remote desktop (a good VNC alternative)
Asterisk - Open source PBX
Video - Various ways to convert and manipulate video files.