Netbeans - NetBeans IDE 7.0. Develop desktop, mobile and web applications with Java, PHP, C/C++ and more. Runs on Windows, Linux, Mac OS X and Solaris. NetBeans IDE is open-source and free.
Kodiak PHP - Kodiak PHP can run any PHP code directly (offline) on your iPad, no need for an internet connection.
Aptana Studio - The world’s most powerful open-source web development IDE just got better. Rebuilt from the ground-up. It's now much faster, customizable and includes new features to help you be more productive.
Rapid PHP - Rapid PHP editor is the world's fastest and lightest PHP IDE for Windows with code intelligence and tools for PHP, HTML, CSS, and JavaScript, including PHP debugger, FTP/SFTP client, UTF-8 support and more.
PhpStorm - Professional IDE for PHP and Web Developers
NuSphere PhpEd - PhpED - PHP IDE integrated development environment for developing web sites using PHP, HTML, Perl, JScript and CSS that combines a comfortable editor, debugger, profiler with the MySQl, PostrgeSQL database support based on easy wizards and tutorials.