I used two books for studying, the first one is "Sun Certified Enterprise Architect for J2EE Study Guide (Exam 310-051)" book which is not that good for studying, but it gives you a very good idea about Architect and J2ee technology in general, but for exam its not that good.
the other one is "Sun Certified Enterprise Architect for J2EE Technology Study Guide" which is simple and precise, and i recommend this book for studying, its short and free from unnecessary information outside the exam objectives, but this book is not covering all the objectives like "legacy systems".
as a conclusion, the first book i mentioned is very good but not for the certification, just for knowledge, but i think reading it is important for people who are not expert as architects. and the second one is good for the exam.
please don't hesitate to ask me any questions about the exam