Yesterday I updated my previous ZCE certificate to the Zend Certified PHP Developer qualification (the new ZCE for PHP 5.5 also got a new name). Since the ZCE 5.3 exam is no longer available and I work with various clients to prepare their teams for these certifications, it was important to me that I keep my own certification up to date. Now I've done that, I'd like to share some resources for others doing the same thing.
Sample Questions Pack
One really important step in preparing for this exam is to get an idea of what kind of questions you might be asked - in terms of the format of the questions and the topics. I have a pack of 70 questions which I use when delivering ZCE preparation courses, but I also sell it separately and it is now updated for PHP 5.5
Edit: This pack was unavailable from December 2014 due to VAT changes in the EU. Keep an eye on my dedicated page for updates.
As well as questions, this includes answers with detailed explanations of how those are reached and links to further reading. There is also some advice about the format of the exam and what to expect on the day itself.
The PHP Manual is fabulous, but sometimes you need a more conceptual explanation. I maintain a bundle of links to blog posts or other tutorials on the various topics involved in ZCE, which you may find helpful to dip into for your own study:
If you find any broken links, or have any resources you think should be included, just let me know. I intend for this to be a living document that we can share.
My advice for cramming for ZCE is always the same: you need to recap all areas of the manual but focus especially on strings and arrays, because while there will be an average number of questions on these topics, it's common to see strings and arrays used in questions that are really about function scope, or inheritance, etc.
For my own revision, I created flashcards by taking the PHP manual and making them into double-sided PDFs that I could cut up and use (you could do this with a single-sided printer, print the odd pages first and then put the paper through again - for duplex printers beware that you need to choose "short side").
Here are the String and Array flashcards that I used for myself (they're not perfect, but I found them useful so if you want to download them, you can. The main omission is that I stripped < and > characters which makes for interesting string comparison documentation).
Hopefully some of these resources will help you prepare for your own professional certification - good luck :)