A cheatsheet for diagnostic and troubleshooting commands that I made for my developer colleagues at Songkick.
We use Ubuntu, so it's mostly focussed on that.
To generate a printable page I do this:
pandoc -f markdown -o cheatsheet.html cheatsheet.md # any markdown processor should work
xdg-open cheatsheet.html || open cheatsheet.html # should work on ubuntu & Mac OS X
I then print it out at two pages per side, which is currently a single side of A4 paper.