1) "Demon Haunted World", Carl Sagan
Essential information on why people believe strange things and how to reliably discover truth based on reason and evidence. Includes techniques/mistakes that are used to try to convince people of things that are either provably false or at best unprovable. I recommend this first because it doesn't address Mormonism directly, but does undermine the credibility of the church's gold standard for finding "truth".2) "Rough Stone Rolling", Bushman
Gives incomplete information on some issues such as polygamy, but otherwise an honest and complete at Joseph Smith's life from the perspective of a believing Mormon. It is much more difficult to question the facts when they are coming from a faithful member who still believes.3) "No Man Knows My History", Fawn Brodie
Same facts from the prespective of a non-believing relative of a church president. Even Bushman cites Brodie's work as being very important.4) "In Sacred Loneliness" Todd Compton
I wouldn't recommend any other Joseph Smith biographies that I've read since they don't add anything to those two and are not as readable or well-written.
The real scoop on the origins and practice of LDS polygamy by Smith and his successors and the effects on the wives. I simply can't understand anyone who can read this book and still believe in a divine origin for the practice.5) "An Insider's View of Mormon Origins", Grant Palmer
Good summary of the issues surrounding the founding of the church.6) "Book of Mormon Authorship Revisited", FARMS
Confirms the facts in the above books such as Joseph using his treasure seeking seer stone to translate. Also shows how weak the case for the Book of Mormon is despite the best attempts of its defenders.7) "By His Own Hand Upon Papyrus"
A complete and thorough debunking of the Book of Abraham. Addresses and refutes all of the theories of the church's apologists. Given that we can with certainty determine that the Book of Abraham is not an authentic translation, then why would we believe in the Book of Mormon?8) All of D. Michael Quinn's books.
May be dry and difficult to read for some, but thorough and well-written.I've read many more, but those would be at the top of my list.
Just for any defenders wondering if I've taken a balanced approach to my studies of Mormonism I'll give the following.
I was fully active in the church for 40 years. I attended church weekly including all of my primary classes, sunday school classes, sacrament meeting, general conferences, general priesthood meetings, stake priesthood meetings, and many others. I also graduated from BYU which included religion classes on the Book of Mormon, Pearl of Great Price, Isaiah, genealogy, Old Testament, etc. I also taught early morning seminary for 3 years after I graduated. As you are aware, the lessons in church classes repeat endlessly and I had the content down pretty well the first time. So, I'm pretty familiar with what the church teaches in its correlated lesson manuals.
I also read quite a few church books. I'd have to check but I'm pretty sure that they were all from Deseret books. No anti-Mormon books in the lot. Among the books was a book on the Pearl of Great Price that was basically a survey of papers. I also read Jesus the Christ, The Articles of Faith, Joseph Fielding Smith's Comprehensive History of the Church (in English and Spanish), A Marvelous Work and a Wonder, The Miracle of Forgiveness, a series of books (5 or 6 in the series) that contained GA quotes related to each section of the Doctrine and Covenants, some short History of the Church book, Mormon Doctrine, Joseph Fielding Smith's Answers to Gospel Questions (or something like that), The Teachings of the Prophet Joseph Smith (by Joseph Fielding Smith).
I guess what I'm saying is that although in recent years I've focused on books that some would consider anti-Mormon, all I was really doing was balancing out a lifetime of pro-LDS apologetic, polemical literature. I believe that these "anti-Mormon" books are actually well researched and balanced. In stark contrast are the publications of the church and in particular FARMS which employ all of the dishonest tactics that the church accuses the anti-Mormons of. The "anti-Mormon" books seem to not need to employ those tactics. I wonder why.
My summary of why I no longer consider myself Mormon is that I discovered that the teachings of the church and its defenders are a completely dishonest, incomplete misrepresentation of the facts. The church consistently suppresses or glosses over its problems and hides those things it can't explain away. The church simply can't handle having a complete, unvarnished retelling of its history because, to put it bluntly, if they told the truth then nobody would believe it.