Phpmole is my lifeblood for development, when I wrote it, I added all the features that where missing from other editors, and the resulting editor made a huge difference to my productivity - code folding, autocompletion, inline help hints, a list of open files, and other standard editor features as well.
However Phpmoles code base is now pretty old, and was written before I did much PEAR work. So I've started hacking on leds, the editor I mentioned before when hacking on D. It has the benefit of being relatively small codebase wise, and very easy to understand. Let alone it's fast and runs as a binary, so I can eventually just compile the lib's and distribute them, rather than a huge array of php files.
This new IDEis mainly built with the programming language D, and, once the basics were out of the way, he integrated a PHP parser (with the help of Zend's lexer). It's not "pretty code", but it works. If you'd like to take a look, check it out here.