One of the good sites to prep for the SCWCD Exam is www.j2eecertificate.com. The only gripe I have about this particular website is that the level of questions regarding the custom tag libaries is not upto the mark vis-a-vis the real exam.
You might also wanna check out http://www.geocities.com/r_palwai/scwcd.htm.
Just my 2 cents. All the very best for your crack @ the SCWCD.