Maguma PHP4EE Studio is the source-code-level IDE, equipped with all the features known from other languages' development environments.
Through tight integration of the PHP interpreter and the PHP documentation, PHP Coder gives developers a time-saving development editor. Features are full integration of the PHP interpreter and the PHP documentation, integrated preview window, full syntax highlighting for HTML and PHP, AutoComplete for frequently used text constructs, tag buttons and all the standard editing functions like almost unlimited undo, copy and paste, searching, etc. And it is quite small compared to other language's IDEs and loads pretty fast.
Maguma AG provides the PHP4EE Studio Light product for free to the PHP community.