I'm working on a project based on cakePHP and I've been looking to have a free - lightweight IDE which assists me along the way.
I tried Aptana Studio, Eclipse PDT, Edit++ and NetBeans.
All but NetBeans are a bit to "heavy" - see Eclipse PDT or the autocompletion is limited to the core php.
Beautiful autocompletion - almost as beautiful as the one from xcode, which btw. can be used for PHP development, but I think is a bit too much for scripting - fast loading and a nice overview of what scripting covers.
So if you're looking for a good IDE for writing your php code, use NetBeans. They offer a package just for PHP about 25MB for free. See all the features here: http://netbeans.org/features/php/index.html
What do you think? Drop a line.