Here is a collection of my favourite cheat sheets that I use
Regex:
My favourite regex cheat sheet can be found below. It includes a brief one page layout showing all of your regular expressions statements including ranges, character classes, string replacement etc. This sheet comes from the wonderful people at http://www.addedbytes.com/
Vi:
For a quick overview of everything Vi related, I suggest the below cheat sheet. This sheet is 2 pages, and contains all of the input, motion rearrangement and search and replace commands anybody could ever need. It does a very good job of condensing all of the data you will need to be proficient at learning Vi
AIX:
The AIX quick sheet is awesome at condensing some of the most used commands in AIX into a front and back cheat sheet. Perhaps not a simple wall reference, this guide includes a heck of a lot of data, and will help any new AIX admin quickly get the hang of things (especially if you have previous UNIX experience)