Boasting almost 14 million posts, Ars Technica is one of the biggest and oldest technical forums still operating today. They use phpBB to power their forums and comment system.
Independent site for Dutch horse lovers. With over 280,000 members and 95 million posts, Bokt.nl is widely acclaimed as one of the largest boards powered by phpBB.
Adblock Plus is one of the most popular Firefox Add-ons in the world, with over 10 Million daily users and over 100k downloads a day. They use phpBB to offer support to their users.
Pixelmator is a popular commercial image editing software for Mac OS X users.
Zend Technologies is one of the largest and most popular companies producing a wide variety of tools and frameworks for PHP. Their community forums rely on phpBB.
Hugely popular Mozilla community providing support for Firefox, Thunderbird, Seamonkey and other well known Mozilla products. Over 350k members and 4 Million posts.