By non-LDS:
Mormon America: Power and Promise, Richard K. Ostling and Joan K. Ostling, Harper, 1999. Very impartial, much better than some explicitly anti-Mormon books or even most books by investigative journalists–the latter tend mainly to be irreligious/secular and miss a lot because of their biases against relgion in general.
Joseph Smith’s Response to Skepticism, Robert N. Hullinger, Signature Books, 1992
Religious Seekers and the Advent of Mormonism, Dan Vogel, Signature Books, 1989.
Two which I recommend only for the evidence which their research uncovered, NOT for the interpretations and ‘spin’ which the Tanners put on that evidence:
The Changing World of Mormonism, Jerald and Sandra Tanner, Moody Press, 1980.
Mormonism–Shadow or Reality?, Jerald and Sandra Tanner, Modern Microfilm Company, 1972.
The only other anti-LDS apologetics work that I am fairly comfortable with:
Reasoning from the Scriptures with Mormons, Ron Rhodes, Harvest House Publishers, 1995.
Several from LDS sources. I really advise people NOT to spend too much time only reading anti-LDS stuff–it is difficult to find material which doesn’t include at least some mistakes or which is tainted by the author’s biases against the LDS Church. If you read anti-LDS material–try to read at least two books by Mormons on the same subject for every ONE book by an ‘Anti’–it will help you keep perspective. Not every pro-LDS book has to be apologetic in nature, but it should help you gain a better grasp of how the same ideas look from ‘inside the head’ of practicing LDS, which is always a help in dialoguing with members of other faith-traditions. :
The Articles of Faith by James Talmage
Jesus the Christ, by James Talmage
**A Marvelous Work and a Wonder **by LeGrand Richards
The House of the Lord by James Talmage (Talmage is a classic LDS writer, greatly revered).
You May Claim the Blessings of The Holy Temple, (alternative title: The Holy Temple), Boyd K. Packer, Bookcraft, 1980
**Church History in the Fulness of Times **distributed by the LDS Church (Church Distribution)
Gospel Principles Church Distribution
An Approach to the Book of Mormon by Hugh Nibley
The Mormon Doctrine of Deity by B.H Roberts (another much-revered classic LDS apologist–who is rumored to have suffered doubts about his Mormon faith in his declining years, btw).
Joseph Smith and the Beginnings of Mormonism, Robert L. Bushman, University of Illinois Press, 1984
Encylopedia of Mormonism (Not suggesting anyone read the whole set but selected articles as needed)
**The Work and the Glory **Gerald Lund (9-volume fictional account of Joseph Smith–good intro to LDS history, and now becoming available on DVD as a series of movies).