The CES Letter is often cited by Church members who lose their faith or non-members who decline to continue working with missionaries. Lots of faithful LDS individuals and groups have posted responses to the CES Letter with varying degrees of success.
One of the better sites does a great job of pointing out logical and factual fallacies in the CES Letter. On most topics, the analysis is excellent.
Unfortunately, the site includes a section on Cumorah that ought to be revised after the author does more research.
The first paragraph is only the beginning of the problems.
The site ignores what the prophets have taught in favor of the M2C theory that certain intellectuals have taught.
A good start is here:
Source: About Central America