If you search for the topic “php performance” in the search engines probably you will get what

you need on the first page. During my investigations around the web I had colected some not so visible and very useful posts and presentations:

12 quick PHP performance tips:

http://www.moskalyuk.com/blog/php-optimization-tips/1272

Enormous collection of slides and presentations about web architectures and scalabilty:

http://www.royans.net/arch/library/

Slideshow about overall PHP performance:

http://talks.php.net/show/hpp/0

40  tips for optimizing your PHP code:

http://reinholdweber.com/?p=3

Useful post about php performance and best coding practices:

http://atomized.org/2005/04/php-performance-best-practices/

Ilia Alshanetsky talks on different tematics, including PHP performance and security:

http://ilia.ws/talks.php