Now bumped to version 0.5.1, the PHP API now has all methods of the MaxCDN's XML-RPC interface implemented. Only thing left is to finish all the unit tests, create an automated build system (for self), throw in a lightweight tutorial and get to work making extensions for various frameworks (WordPress, Drupal, CodeIgniter, CakePHP, etc).
If you'd like to grab it now, head on over to GitHub and checkout the latest commit. You can feel free to use this in your project as it is MIT-licensed. Hack away, report any bugs on the GitHub project (yes, I am using GitHub Issues as its issue tracker) and let me know any other comments you have for this.