List of my favorite Quick and Customizable Reference Sheet of Flash, Web 2.0 Application and More!
ActionScript Reference Sheet
ActionScript 2.0 Cheatsheet
ActionScript 2.0 to 3.0 Migration Cheatsheets, (Multi-Page PDF)
ActionScript 3.0: Top Level Cheatsheets, (Multi-Page PDF)
ActionScript 3.0: flash.display Package Cheatsheet
ActionScript 3.0: Packages Cheatsheet
ActionScript 2.0 Cheatsheet
Flex
ActionScript 3 API PDF at Flex.org
Flex 2 Framework API PDF at Flex.org
Ajax Reference Sheet
What’s Ajax? Cheat Sheet – PDF
Prototype Dissected – Cheat Sheet PNG
scriptaculous Combination Effects – Cheat Sheet – PDF
Adobe
Apache Reference Sheet
CSS Reference Sheet
CSS 2 – Quick Reference Guide – PDF
HTML/XHTML Reference Sheet
A Simple Guide To HTML – Cheat Sheet
HTML & XHTML Tag Quick Reference
XHTML Cheat Sheet v. 1.03 – PDF
JavaScript Reference Sheet
JavaScript and Browser Objects Quick Reference
Regular Expressions for JavaSript – free online quick reference
Joomla Reference Sheet
MySQL Reference Sheet
PHP Reference Sheet
symfony PHP5 framework – Admin Generator cheat sheet – PDF
PHP Cheat Sheet with special php syntax
Regular Expressions Cheat Sheet – PNG
WordPress Reference Sheet
Web Design WordPress Template Tag Reference Guide
Note: Some of the list courtesy by SmashingMagazine.com