Justin Silverton has a list on his blog of some of the PHP-based games out there today, including several RPGs and various smaller, lighter games.

The list includes:

• Heros of Might and Magic
• Anoi Towers
• Chipmunk Riddles
• Legend of the Green Dragon

Not all of them are smaller, independant sites either - the Heroes of Might and Magic site is related to the widely popular Ubisoft game of the same title. Always great to see PHP being used in major ways!