Cheat-Sheets.org is the only place I have been visiting for any quick reference, not only for Linux, but also other programming and web developments languages. They even have cheat sheet on chemistry topic?!

Quoted from there, these are the Linux cheat sheet you might need.

• Linux Command Line Tips [html] (pixelbeat.org)
• Linux Shortcuts and Commands [html] (linuxshortcuts.shtml)
• Unix/Linux Command Cheat Sheet by Jacob [pdf] (fosswire.net)
• The One Page Linux Manual by Squadron [pdf] (homepage.powerup.com.au/~squadron/, digilife.be)
• Linux Administrator’s Quick Reference by Jialong He [pdf] (tiger.la.asu.edu)
• Linux System Calls Quick Reference by Jialong He [pdf] (tiger.la.asu.edu)
• Linux Security Quick Reference by Dave Wreski & Benjamin Thomas [pdf] (tiger.la.asu.edu, digilife.be)
• screen Quick Reference [html] (aperiodic.net)