Tips from a graduate who has recently taken the exams:

When you are ready to take the Architecture Registration Exams, you can find study material through your firm, on Craigslist or used textbook sources, or on kaplan.com. Not all firms have this costly material available to you, so you may need to get creative to cut costs. Use NCARB as a resource (for free). Also, check Craigslist or Kaplan for the 4.0 version of the material.

As far as the Kaplan materials, the study guide itself is the single most valuable study resource. The study guide has a good overview of the test material, quizzes at the end of each section, and a final sample quiz at the end of the book. The study guides cost $70 to $80 each, based on Kaplan's web site. Buying and reading the guide for each test will put you in pretty good shape. 

The "questions and answer book" is also a good resource ($35), especially for some of the denser tests (Structures, Systems, CDs, BDCS). They have something like 200 practice multiple choice questions, in addition to what you get in the study guide. In my experience, the flashcards, online things, and other materials were all pretty useless. 

NCARB has a brief overview, sample quiz (which is more like the actual test questions), and practice vignettes (Practice Program) on their website. You should take a look at and download the practice test: http://www.ncarb.org/en/ARE/Preparing-for-the-ARE.aspx. The study guides here are not very helpful, but the practice program is great in preparing you for the drawing portion of the exams. 

Typically for each test, I read the study guide, did the practice exams in the guide, and then did each of the practice vignettes NCARB has on their website, and I found that prepared me pretty well for the exams. 

Good luck!