The last few weeks I've had to dive into Linux again (to install a wiki), and I found some more cheat sheets and tutorial that were helpful:

• LinuxBasics offers attractive tutorials on a number of topics, nicely organized.
• The Filesystem Hierarchy Standard explains all of the details of the layout of a typical Unix box. Don't know the difference between /usr/sbin and /var? This comprehensive standard has the answers.
• YoLinux's Linux System Administration Tutorial was very helpful.
• The O'Reilly Linux devcenter has an Alphabetical directory of Linux commands, if you need the details of a particular command.

Finally, this won't help you run a Linux box, but Éric Lévénez's UNIX History has a mind-blowing graphic laying out the entire twisted family tree, from September 1969 to the present.