I have spent the last 6 months preparing, and just wrote the exam on Saturday (fingers crossed).
Here are my essential sources of information:
- all the exam related material on the BJCP site, including the Study Guide (very helpful)
- Ray Daniels' "Designing Great Beers" (great book for styles, history, and recipe creation, including the technical aspects of the methods for calculating things like grainbills, gravity, bitterness, etc.)
- Jamil Zainasheff and John Palmer's "Classic Beer Styles" - great crash course in the different styles and sample recipes (very important resource!)
- Greg Noonan's "New Brewing Lager Beer" - all you wanted to know (and more) on brewing techniques and the science behind brewing
- any beer guide by Michael Jackson that you can get your hand on (the BJCP style guidelines are fine, but mostly technical -- Jackson's book bring them to life and are an essential reference for describing beers)
There are lots of other materials that are helpful (e.g., John Palmer's "How to Brew", George Fix's "Principles of Brewing Science"), but the ones above were my 'go to' references. Unfortunately, I didn't have the benefit of a course so everything was self-study, which is totally possible (I hope). But it would be good to get together with some experience judges and go through beer evaluation with them (that was my weak point).
Anyways, the BJCP is a great program for promoting beer appreciation and beer evaluation skills. Highly recommended program.