JetBrains has their annual sale where they offer PhpStorm for $49. This is a good time to pick up a really good IDE for PHP. I’ve used many different IDE editors for PHP including NuSphere PHPEd, Eclipse, and NetBeans. The standout features for PhpStorm are the speed, cross-platform compatibility (OSX, Windows, etc), and intelligent code completion for classes and methods. It really helps speed up development time when you have a large codebase. Another nice feature with PhpStorm is the built-in Git integration. At 50% the regular price of $99 — its a great deal for $49.
Update 9/20/2012 – Sale ended. They now offer a new $29 academic license option for students.