First of all, I'm an Oracle Certified Professional, Java SE 6 Programmer.
I've noticed that there are two Web Services certification exams: OCE, Java EE 6 Web Services Developer Exam and the OCP, Java EE 5 Web Services Developer Exam. Which one do you suggest that I take? What are the differences between the exams besides the different versions of Java? Should I take the OCE, Java EE 6 Web Services Developer Exam since I'm already certified in Java 6?
I always advice to take the latest version of a certification exam. There are a number of differences between the EE5 and EE6 exam. You might want to check the exam topics from the official oracle certification site or read some of the stories of people who passed the EE6 version of the exam lately (check the Certification Results Forum)
I must warn you that the WSD exam is quite tough and totaly different from the OCPJP6 exam. You might want to consider doing the WCD6 and EJB6 exams first as a couple of questions come from these exams. Apart from that, for the WCD and EJB exams reading and studying one book and some parts of the specifications is enough whereas for the WSD exam you have to gather a lot of materials to prepare yourself.