There are tons of books and tutorials on PHP, MySQL, Zend, and SEO on store shelves. There are even more resources found only on the internet. Sometimes you need something in the middle, content you can download legally and keep handy when you are offline. Below are a few completely free resources that most beginner or intermediate web developers (even if you do it just for yourself) will find useful.
PHP
1) PHP Reference: Beginner to Intermediate PHP5
Shameless self-promotion. A reference for many of the functions within PHP that serves as a quick go-to resource for checking syntax and remembering the nuances of many of the functions. It is available as a PHP book you can purchase in print, however the entire book is released under creative commons and available as a PHP reference PDF.
2) Object Oriented PHP Tutorial in PDF
Provided by killerphp.com and Stefan Mischook, this is a PDF version of his article on the topic of object orientated programming in PHP. It gives a conversational explanation to the basics. More information and the OOP PHP PDF is available over on killerphp.com.
3) Zend Framework: Surviving the Deep End
The Zend Framework can help developers organize and write more efficient PHP code for large projects and has become one of the top frameworks used online today. From the page…
“The book was written to guide readers through the metaphorical ‘Deep End’. It’s the place you find yourself in when you complete a few tutorials and scan through the Reference Guide, where you are buried in knowledge up to your neck but without a clue about how to bind it all together effectively into an application.”
While available online, there is a link to downloading the PDF version in the bottom right. Check out the Zend Framework survival guide.
HTML, CSS, AJAX
4) The Woork Handbook
Another compilation of online articles compiled and organized as an offline document. From the page…
“The Woork Handbook is a free eBook about CSS, HTML, Ajax, web programming, Mootools, Scriptaculous and other topics about web design… directly from Woork!”
This isn’t a full study of any single topic, but is filled with tidbits. Grab the Woork Handbook.
5) Added Bytes Cheat Sheets (formerly ILoveJackDaniels)
While the site’s name has changed, the great resources have not. Cheat sheets are designed to cram (in a useful way) tons of information into the front and back of an 8.5″ x 11″ sheet of paper. There is little excuse for not keeping these handy. Grab the cheat sheets for HTML, CSS, RegEx, Mod_Rewrite, and more.
MySQL
6) MySQL Manual
All MySQL documentation is available as a downloadable file. Choose from various options for the MySQL documentation.
Editor’s Note: I had trouble finding a good, free, legal resource for MySQL that wasn’t hyper specific and was user friendly. I hope others have suggestions they can leave in the comments.
SEO (Search Engine Optimization)
7) Beginner’s Guide to Search Engine Optimization
SEOMoz.org is an amazing website for learning the complex world of SEO with a very clear, user-friendly tone. Besides that, they offer a bunch of tools for helping your new website get better in the eyes of search engines (aka Google). Available as HTML, MS Word, or an OpenOffice document, you can get a copy of the Beginner’s Guide to Search Engine Optimization over on SEOMoz.org.