Studying to become a Magento Certified Developer
All questions are multiple choice. Moreover it's also indicated in a question itself how many answers it has, for example, "What is this class responsible for in Magento" - it means that the right answer will be only one, "Which two of the following you must do to achieve something" - and you should choose two answers.
I would recommend to start with the Fundamentals of Magento Development Video Course. It covers more than half topics from the Study guide. So before each chapter you can watch these videos and then start digging.
Students will leave the course understanding the Magento architecture, MVC and data models, how to work with Magento modules, and how to customize and extend Magento to ensure the best upgrade path for the websites they extend
There is also a Study Group Moderator’s Kit you can get for a nominal fee. There is a set of exercises on different topics with code sample answers. This could help you not only to prepare for the certification, but also enrich your knowledge in general.
Since the Study Group Moderator's Kit isn't available anywhere, Vinai Kopp made an excellent, free resource: Grokking Magento: Book 1 - Magento Basics & Request Flow. This is an in-depth ebook on the study group material.
At BelVG we have a certification dedicated category in our blog. At the moment it covers only the first chapters, but we're working on it.
Magestore also has a lot of articles.
But the real way to prepare for exam is: all questions in certification guide have the following info:
These code references can be used as an entry point to find answers to the questions above
Essentially it's a list of files/classes that need to be examined. There is no magic pill - you need to open all of them and check all main methods and analyze how they work. We spent 2-3 hours after work within 3 months to prepare for exam...
As additional info you can check, as mentioned here, Alan Storm articles, Knowledge Base, Magento Extension Developer’s Guide and Design Guide
Disclaimer: I passed exam in May of 2012, and it was based on Magento CE 1.5, from January of 2013 it's based on Magento CE 1.7 and I think that they should update Certification Guide.
Now, In 2016 it's based on Magento CE 1.9
I took the exam at the end of 2012. Unfortunately, I missed the passing mark by two questions. =(
My best advice is to study the areas you feel you would do poorly in. For me, this was EAV and Database (I mostly work front-end, so this is an obvious weakness for me). I did fair enough in most sections, but completely bombed these two sections. Knowing this now, I would have spend more time studying these weak points. Had I spent just a few more hours here, I am sure I would have passed easily.
While the reference materials others have suggested are good, the best reference material I had access to were the Magento U books provided by @Benmarks. While they are not going to flat out tell you the answers (sometimes they do) they give you the information you need to figure it out. They also highlight a number of quirks that many people might overlook (such as app/etc/local.xml being loaded both first and last, which is definitely on the exam).
Study groups also help. If you have others around you that can meet in person several times for a few hours, you will really help each other out. I know I would have done better on the exam had I been able to study with others who do more backend development.
http://www.magestudyguide.com/
This link is also very helpfull for study guide, it covers all question which are in study guide pdf, and explain question in brief.