Here’s a very handy resource for webmasters I came across a while back. Free Cheat Sheets in PDF and PNG formats covering the following:

MySQL Cheat Sheet
A quick reference guide for MySQL, including functions (both in MySQL and PHP), data types, and sample queries.

mod_rewrite Cheat Sheet
A quick reference guide for mod_rewrite, including server variables, flags and regular expression syntax. Also includes examples of commonly-used rules.

CSS Cheat Sheet
A quick reference guide for CSS, listing selector syntax, properties, units and other useful bits of information.

PHP Cheat Sheet
I’m fed up with having to visit php.net to look things up. This A4 cheat sheet is designed to sit by your desk and make your life easier.

RGB Hex Colour Chart
A free, printer-friendly RGB Hex colour chart for web designers.

I have them sat on my desktop, and they are genuinely useful when you can’t for the life of you remember that “bit” you need.