PHP: 6,930,758 Domains, 957,249 IP Addresses
Source: Netcraft
The drop-off in August is related to the .com crash with a number of sites and ISP's disappearing. Netcraft's total number of sites found dropped in August from 31,299,592 to 30,775,624. PHP's percentage actually rose from 22.2% to 22.4%. In September the numbers are back up somewhat. Netcraft found 32,398,046 domains and PHP's marketshare percentage has dropped to 21.4%. This is mostly due to the fact that homestead.com sent Netcraft their site list of over a million domains running IIS.
You can also see how popular PHP is relative to other Apache modules at . Spoiler: PHP is the most popular.