On PHPMaster.com today there's a new tutorial showing you how to generate API documentation with the help of the ApiGen documentation tool and some commenting in your code.

If you’re writing undocumented code, you should stop this very moment. I’m serious. Drop everything, save and quit, and focus on improving this essential part of your workflow. [...] ApiGen is a docblock parser like PhpDocumentor. PhpDocumentor has been around for much longer than ApiGen, but unfortunately its development is somewhat stunted and it lacks in terms of modern documentation and examples.

He shares an example class, fully commented to show off the right way to handle the DocBlocks and goes through each of the "@" types and explains what they're for. Also included are the instructions for getting ApiGen installed (via the PEAR installer) and a sample command to generate the docs from the source. You can find out more about ApiGen and some of its other options on it's main site.