There ain't no such thing as a free IDE for PHP that doesn't suck.

'Nuff said, but you'd probably like to know why I say this in my curmudgeonly fashion. First of all, a disclaimer: Text editors with highlight support do not an IDE make, even if they give you a task pane of files. Second, I'm writing this from a Windows perspective; any PHP IDEs that don't run on Windows are useless to me.

Currently, for work, I'm using Eclipse PDT. Despite being written in Java, it's actually somewhat responsive and not sluggish like most Java programs I've encountered. It's also extendable through various plugins, which is how I have Subversion integration. Still, it does annoying things like have five or more different solution view panes (as opposed to two for Visual Studio) of which only the ones with names starting with PHP are of any use. Revision information bloats the "PHP Explorer" view, making it difficult to read filenames without actually opening the files and looking at the title of the tab for that file. And, while it might be a Vista thing and not Eclipse, views enjoy automatically scrolling horizontally when I try to read what's there.

On Rob's suggestion, I took a look at Aptana Studio, which he apparently uses for work doing Drupal development, without problems. It's built on Eclipse, but is shinier and perhaps a bit slimmer, UI-wise. All good and well, except that it doesn't want to work with Subclipse (it installs, but I can't use it from a solution view the way I can in Eclipse). That Subversion support is a deal-breaker, so if anyone from Aptana is reading this, get back to work and make Subclipse play nice!

Last of the free IDEs (well, kind of) is Visual Studio with Phalanger, a .NET compiler for PHP. Phalanger offers Visual Studio integration, which works fine so long as you have all your project files in a single directory. Otherwise, it breaks in strange ways. Considering that it uses the MSBuild engine, which has no problem with project files all through a tree, I can't fathom how they broke things like this.

I've not tried any others, although I know about Dev-PHP (not updated in a year), and there might be a few other free ones out there. As for the paid ones, I'm not paying for Zend Studio as it seems to be a themed version of Eclipse PDT, and I've heard nothing but bad things about VS.Php.