From peers, administrators, and current CRNAs, the consensus is that the Valley Review is the gold standard. Have not heard anything bad about the Valley review, some programs require students take the review course as part of the curriculum. Will keep an ear out for any others, but hey if its not broke don't fix it. Don't know anything about problems with the cert exam.
What were the problems/issues with the cert exam?
Link to Valley:
http://www.vaep.com