Becoming a Zend Certified Endineer ZCE
A certification exam costs $125. First, I used the book with practice tests for php 4, but it's obsolete now.
Zend PHP 5 Certification Study Guide
is more useful because it has information on all topics included in the exam.
I bought a pack of 10 exams for Vulcan Certification Simulator,
but was very disappointed when I found that most questions are the same in all exams.
I would say that the real Zend exam is very difficult.
Zend Framework
I'm looking forward to buying a new book Zend Framework in Action.
It's written by an author of the excellent introduction tutorial.
It's only a few pages but includes every small detail to start an application with show, edit, and delete capabilities.
Other tutorials are outdated.
Zend Framework in Action - information about Zend Framework.