I've been programming with PHP for many years and have used a lot of editors and so-called IDEs, I must admit that PHP IDEs have become much better now and they differ significantly from simple editors with syntax highlighting. Anyway, in the recent time I have been working much with Visual Studio. I must confess that I really love it, some people may argue of course, especially Java developers who are fond of their development tools and tend to look down at other ones. So, I was happy to learn that there is a plug-in that enables you to program with PHP in a familiar development environment of Visual Studio. Sure, I doubt that it will interest people who don't have Visual Studio, but for developer who are used to it, it's a great choice, I think.
It offers solution and project management, IntelliSense, built-in Apache and PHP (you can work with an external server as well), DBG and xDebug debuggers I especially love its debugging features because I deal with the Visual Studio debugger that I love very much. I suppose VS lovers are going to appreciate this feature.
So, if you are a programmer who use Visual Studio and love it and have to use PHP as well, then I think you should give VS.PHP (yeah, that's how it is called) a try. It's available for both Visual Studio 2005 and 2008. There is a 30 days trial. While the full version costs only $99.99 that is not that much comparing to other PHP IDEs, like Zend Studio or NuSphere PHPEd.
I almost forgot to mention, it has built-in Zend Framework as well :-)!