PHP Eclipse
In the free and open source space, PHPEclipse http://www.phpeclipse.de/ is a better PHP plugin for Eclipse than PDT.
PHP is wildly popular in the open source community, but less so in the enterprise. These things are hard to measure, but one indicator is job vacancies. According to ITjobswatch, there are nearly four times as many jobs for ASP.NET developers as for PHP, and even more for Java. PHP sponsor Zend Technologies wants to change that …