The beta version of the exam blueprint suggests two recommended official training courses:
vSphere: Fast Track [v5] - available now
vSphere: Optimize and Scale [v5] - due in the summer of 2012
This training won't be compulsory in order to qualify for the VCAP5-DCA certification, but having seen the beta exam blueprint, and knowing the Fast Track content and the Optimize and Scale topics, the training courses will definitely be useful!