I am planning to take SCWCD exam (310-083).... I am going to refer Head First Servlets & JSP by Kathy Sierra. Is it a good book for gaining in-depth knowledge and scoring good marks? Do you guys suggest a better book (if any) than HFSJ?
I think the Head First is a good book, but may not be enough to pass the exam with high score. I would recommend referencing Servlet 2.4, JSP 2.0, JSTL specifications in your preparation as well. The JSP syntax is also a good reference: http://java.sun.com/products/jsp/syntax/2.0/card20.pdf
Don't worry about reading all those specs, occasional referencing is good enough. For me, I only referenced them for the relevant information when I felt the cover in the book is inadequate, or when I though the mock exam is incorrect.