In Apache Zeta Components and in several of my own projects we are using - so called - struct classes to solve this issue: The struct classes do not define any methods but just contain documented properties. They just deal as a data container, similar to a hash map.

He mentions a few benefits and drawbacks to using this approach including the fact that, while they're easier to document and can make things clearer in your IDE, they also are objects and are passed by reference by default (leading to possible unintended behavior). That being said, he includes a sample implementation so you can judge for yourself. The example defines a Location with a city and state properties that extends a base Struct class.

He looked into several of the methods out there, but wasn't pleased with any of them - so he created his own, the Phly_Struct and Phly_Config modules. He talks briefly about what they are, but gets quickly into the code examples to prove their worth. It's a basic example tying the two of them together and loading some simple values into an instance of the Phly_Config. Both are available from the PHLY: PHP Library PEAR channel.