The Cicerone Certification Program recently released recommended "Key Resources" you need to study to pass the exam for every level of the program - Certified Beer Server, Certified Cicerone, Advanced Cicerone, and Master Cicerone.
First, I've created my excellent Beer Scholar Study Guides for the Cicerone Exams that have helped hundreds of people pass the CBS and CC exams. Seriously consider picking up my Guide in addition to any other reading you do. It'll save you time and effort. My Guides follow the CCP's syllabi and summarize all the info you need to know to pass the exams, plus offer detailed breakdowns of the test sections and tips and tricks for beating them.
Now, let's look at what study resources the CCP recommends for the first level of the program, the Certified Beer Server (CBS). The CBS exam is an online exam that tests a basic level of beer knowledge and as such test takers are not required to learn a ton of material. In general, the CCP says: "while it is not mandatory to review all of these resources in preparation for our exams, we hope candidates can utilize this list in conjunction with the syllabi to focus their studies." I would recommend that you read and study all of these resources, as merely passing the test isn't the only point, you also want to become a beer expert, too!
CCP Recommended Key Resources:
Tasting Beer: An Insider's Guide to the World's Greatest Drink by Randy Mosher
Grab the CBS syllabus so you know what to pay attention to in these resources.
Additional resources I recommend:
Again, my own Beer Scholar Study Guide for the Certified Beer Server Exam contains everything you need to know to crush the test.
The Cicerone Certification Program's Beer Style Flashcards are great for learning all the beer styles you need to know. Note that these are only good for the CBS exam, not the CC exam. Also, FYI there are free sets of flashcards for the Cicerone exams online, but every one I've ever looked at are full of errors and info you don't actually need to know, so stick with sets from folks like me or the CCP, just sayin'!