According to the TIOBE Programming Community Index (updated once a month) PHP is not only the most popular module for the Apache Webserver but also one of the most popular programming languages. With the highest "Delta 1 Year" (indicates the changes in ratings for the last 12 months) and "Status A" (denotes mainstream languages), PHP is growing fast, really fast!! Thanks to Sebastian for the link.

In this link from PHP Magazine, there is a chart showing the major languages and how popular they are, as well as how much that rating's changed over the course of the year. PHP, thankfully, seems to be on a constant rise - currently at +6.49 for the year.