Whilst the new VCAP4-DCA exam is 100% live labs, so hands-on practice and experience are a really key part of any preparation for the exam, there are already a number of key study resources available.
I have various other blog posts on VCAP4-DCA already, with links to the key official and unofficial resources such as the exam blueprint and some experiences of those who took the beta version of the exam.
Sean Crookston over at vFAIL.NET has been busy collecting together information about most of the elements covered in the VCAP-DCA exam into a set of posts on his site, so here is his VCAP4-DCA Index.
Update: October 15th 2010
The vFAIL.NET Study Guide is now complete, and will be available soon as a downloadable PDF