A couple articles that are really just a collection of tips and tricks for the command line and a few other programs. A lot of the stuff I know I wouldn't use, but there is plenty of material here to make using Linux a little easier.

Found at TuxRadar.

Linux Tips Every Geek Should Know - A haphazard list of tips and tricks worth browsing through.

More Linux Tips Every Geek Should Know - Another haphazard list of tips and tricks worth browsing through.