NuSphere phpED: Products: NuSphere: Here’s a sharp-looking development package for PHP/MySQL. It includes an IDE, debugger, GUI for the database, etc. Nicely done for $299.
Buggy as hell. Try TruStudio's old release for Eclipse, WebStudio: http://www.xored.com/download.php Their development is going slow but what they have now is stable.
For good debugging, and the least crash-prone of the IDE's I've tried, try Maguma Studio Lite: http://www.maguma.de
ActiveState's system also has a very nice PHP (and Perl and Python) IDE: http://www.activestate.com