PHPEdit - A full featured PHP IDE for Windows. It has code insight, code completion, syntax-highlighting, integrated debugger, code browser, keyboard templates. [Commercial] - http://www.waterproof.fr/
PhpED IDE - An integrated development environment (IDE) for PHP for Windows and Linux. It supports PHP software development on all stages including coding, debugging, profiling and publishing. By NuSphere. [Commercial] - http://www.nusphere.com/products/
PHPEclipse - IDE built as an Eclipse plug-in. It takes advantage of a robust and widely used application framework. Wiki documentation and IRC support available. [Open source, CPL] - http://www.phpeclipse.de/tiki-view_articles.php
PHP Expert Editor - An easy-to-use PHP IDE for Windows (98+). Has an internal HTTP-server and Debugger to run, test and debug PHP scripts. Website also offers other commercial charting software. [Shareware] - http://www.ankord.com/phpxedit.html
MPSoftware: PHP Designer 2007 - IDE offering editing tools including full support for PHP 5.2, syntax highlighters, nested code completion, code tips displayed as you type, a project manager, code snippets, and built-in code libraries. [Commercial] - http://www.mpsoftware.dk/phpdesigner.php
Maguma Workbench - A customizable IDE with modular plug-in architecture for the development of PHP scripts. They also offer two studio versions: a commercial and an open source. [Commercial] - http://www.maguma.com/
HateML Pro - PHP IDE with built in debugger, CodeBrowser, FTP client and MySQL manager. Features, downloads, issue tracker and forum available. [Freeware] - http://migajek.com/
Eclipse PHP - Developed by Zend and IBM, an IDE which focuses on the development of complex PHP-driven web applications. The Eclipse site also offers IDEs for other other platforms such as Java. [Commercial] - http://www.eclipse.org/pdt/index.php
Dev-PHP - A full-featured IDE for PHP on Windows. Features include Function browsing and full integration of the PHP parser and the PHP-GTK library. [Open source, GPL] - http://devphp.sourceforge.net/