sun certified java programmer (310-025)
The things you have to know for passing this certification is essential for every Java programmer. In my opinion, before you prepare for the exam you should have practical experience with programming in Java for at least a few months. I recommend you then buy the book Complete Java 2 Certification Study Guide by Philip Heller and Simon Roberts. If you understand everything written in this book you will certainly pass the multiple-choice test. Taking as many mock exams as possible after reading the book will make you feel much more confident when going for the test. Many details concerning all aspects of the SCJP certification process can be found at the Javaranch website.

sun certified java developer (310-027)
This certification is a great way to challenge your programming and design skills. In my opinion, before you start working on the assignment you should be familiar with the Java programming language, object-oriented principles, class design, and testing. I recommend you start with the deprecated methods and then implement the generic search method after reading Sun's Collections Tutorial. Once your done with that make sure you really know about Java threads by reading the excellent book Java Threads by Scott Oaks and Henry Wong. Now you are ready to implement the record locking mechanism. Before starting the client-server communication part read Sun's RMI tutorial and Javaworld's RMI articles. After that, you are well enough prepared to implement the server. Now the GUI remains to be done. Get in shape by reading Sun's Swing tutorial and keep special focus on the table and model issues and all other features you want to incorporate into your GUI. Once the functionality of the assignment is complete, make sure your classes are packaged meaningfully, contain all necessary Javadoc comments, and conform to Sun's Code Conventions. Once you have written the design document you should be ready for submission.

sun certified java web component developer (310-080)
The things you need to know for this exam are essential when you develop web applications using Java technology. In my opinion, at least a few months of practical experience with programming servlets and jsp are necessary before starting to prepare for the exam. Also, make yourself familiar with a servlet container like Apache Tomcat. I recommend the book SCWCD Exam Study Kit by Hanumant Deshmukh and Jignesh Malavia as your study companion. The servlet 2.3 specification, jsp 1.2 specifiaction, webapp dtd, and taglib dtd are very valuable for preparation and reference purposes. More infos, links, and mock exams can be found at Javaranch SCWCD FAQ and Javaranch SCWCD Links.