Here are 10 most useful cheat-sheets for a web developer. #10 CSS Cheat Sheet by Added Bytes #9 XHTML Cheat Sheet by Florian Schmitz #8 SEO Cheat Sheet by SEOmoz #7 Javascript Cheat Sheet by Added Bytes #6 Firefox Cheat Sheet by Leslie Franke #5 mod_rewrite Cheat Sheet by Added Bytes #4 PHP Cheat Sheet / Ruby on Rails Cheat Sheet / Python Cheat Sheet #3 MySQL Cheat Sheet #2 Prototype.js Cheat Sheet / jQuery Cheat Sheet #1 Regular Expressions Cheat Sheet by Added Bytes I use most of these cheat sheets personally and find them extremely useful. The Cheat-Sheets are very well formatted and print friendly. There are plenty more useful ones (e.g. GIT Cheat-Sheet) available which I have not made a mention of. If you find other very useful cheat sheet for web developers do leave a comment.