CES Letter
I will tell you right now, the CES Letter has been - and easily so - debunked over and over again.
However, I will also warn you, that the CES Letter's weapon is not information and knowledge. The CES Letter's weapons are emotional reactions and mental stress. Because of this, my warning is that you may need to guard yourself against these deceptive, but effective, weapons. Doubt the CES Letter's claims first, before you doubt your testimony. If you do I promise that you will see the claims in the document fall like dominoes on the deck of a ship.
I have watched, from the beginning, the advent and progression of the CES Letter and I have seen the sophistry and disingenuous effort falter at every attempt to produce anything that can be considered honest or real.
This video gives you a good introduction to the way the CES Letter works, the difficulty it causes, and how weak its claims are.
Sarah Allen 60+ Answers
In over 60, well researched and in depth, posts Sarah Allen reviews the claims of the LDS letter.
Her work shows how much effort it takes to answer questions, as opposed to asking them.
The CES letter throws out a barrage of so-called-questions, knowing that answer the "questions" will be much harder than asking them. Mrs. Allen has done the work to give the answers.
Collection of Responses
This website collects information from across the web and compiles it into one easy to navigate place.
The resources here provide rebuttals, debunking, and clarifications of the claims made in the CES Letter.
Everything from a full PDF report to a vast collection of videos, this library is extremely helpful.