Ben Scholzen has written up a post about how regular PHP arrays can be used as a native configuration option for your applications.

I was asked many times how I organize my config files, and my response was always the same, until some time ago when I switched began refactoring the codebase of my blog. [...] Looking at [the advantages of PHP config files], you may ask now why not everbody is using them. Well the problem mostly is that you cannot create extend-sections (when working with Zend_Config for example).

He compares an example of a method that, using a base config file with some "smarts", you can have it automatically pull in certain files and overwrite settings from the array inside. A sample "other config" file is also included, showing the definition of some PHP settings, resources and database information.