My .NET-using colleagues all use a Visual Studio add-in called Resharper. It adds a ton of features for code analysis and navigation that would be great to see come to PhpED over time. Check it out:

http://www.jetbrains.com/resharper/index.html

Interesting, but what else does it provide other than what is already in PHPEd (watches, evaluations, variable list, etc.). That resharper website states how great the tool is and that every developer needs it, but it doesn't really explain well what it actually does.

Click 'Features' at the top of the page, in the main navigation.

Yes, there is some stuff there that's already in PhpED, but there's quite a bit that isn't, such as some code refactoring and analysis features. Being that it's a C# and VB tool, most of it doesn't apply directly to PHP as a language, of course, but in most cases there are equivalent features that could be done with PHP.