Create Server Daemons with PHP!!

http://kevin.vanzonneveld.net/techblog/article/create_daemons_in_php/

Caching your output with PHP

http://www.theukwebdesigncompany.com/articles/php-caching.php

10 tips every PHP newbie should know

http://www.phpbuilder.com/columns/vaska20050722.php3?aid=948

Learning Object Oriented PHP

http://www.killerphp.com/tutorials/object-oriented-php/index.php

eAccelerator PHP Accelerator

http://www.leigeber.com/2008/04/eaccelerator-php-accelerator/

RRDtool - Open source graphing for PHP and other languages

RRDtool is the OpenSource industry standard, high performance data logging and graphing system for time series data. Use it to write your custom monitoring shell scripts or create whole applications using its Perl, Python, Ruby, TCL or PHP bindings.

http://oss.oetiker.ch/rrdtool/

Blocking dodgy referrers and blocking specific IPs with PHP

Here ya go:
http://perishablepress.com/press/2009/04/21/4g-ultimate-referrer-blacklist/
http://perishablepress.com/press/2009/06/08/block-multiple-ip-addresses-with-php/

Write your own facebook app using PHP !!!

http://www.merchantos.com/makebeta/facebook/facebook-php-tutorial/

reformat date in PHP so it's more readable

http://www.handyphp.com/index.php/PHP-Resources/Handy-PHP-Functions/reformat_date.html

a "firewall" for your PHP applications

http://munin.xqus.com/about

First steps with Ming (for creating flash movies on the fly with PHP)

http://www.ibm.com/developerworks/library/os-php-flash/index.html

Backup your database to an XML file using PHP

http://davidwalsh.name/backup-database-xml-php

PHP secure mail form

http://www.tutorialtastic.co.uk/tutorial/php_mail_form_secure_and_protected

PHP Excel Reader

http://mattkruse.com/2008/12/24/php-excel-reader/

Connecting to WMI with PHP

http://www.aspfree.com/c/a/Windows-Scripting/Connecting-to-WMI-with-PHP/

PHP - Smart image resizer (JPG, PNG, GIF)

http://shiftingpixel.com/2008/03/03/smart-image-resizer/

Read / Write to Serial port using PHP

http://www.easyvitools.com/phpserial/index.html

Bot detection with PHP

http://www.goodphptutorials.com/out/Bot_Detection_with_PHP

some PHP abilities you may not know about

http://www.davidjeffries.com/some-php-abilities-you-may-not-know-about

Google Style "Did you Mean?" with PHP

http://css.dzone.com/news/google-style-did-you-mean-php