If you don't already you should get familiar with Aptitude (apt-get). There's nothing like hopping into the command line and immediately installing the piece of software you want.

I like the Clementine music player.

Being able to hop into the command line to process text is neat. You might want to do a toutorial on grep, awk and sed.

Gimp is nice for photo manipulation, I use Inkscape for vector graphics.

Opera is a nice second browser (chrome is a memory hog) it also has built in vpn and Adblock.