I just started preparing for the exam. There is no specific book to prepare for this exam. However, the book 'Java Web Services Up and Running - Martin Kalin' covers good deal of content for certification. In addition to that use Metro to practise web services. You can try out free mock exams over internet or you can buy mock exams from Whizlabs or any other vendors.
Sai Surya, SCJP 5.0, SCWCD 5.0, IBM 833 834
http://sai-surya-talk.blogspot.com, I believe in Murphy's law.