It first depends on what topic interests you. I think unbiased sources exist when it comes down to physical science. For example, most of the DNA and language studies to determine the origins of Native Americans were approached with no reference to the Book of Mormon whatsoever. Also look at Reformed Egyptian, archaeological sites from the Americas and what they've found and not found. The scientists didn't want to prove or disprove any of the Church's doctrine, they just wanted to know what was supported by the research. So those are probably the most unbiased sources you can find - peer reviewed scientific articles by people who have nothing for or against the Church.
- Dr. Susan Black on Joseph Smith's personal history. She is very active and teaches at BYU currently. She really knows the facts, but also puts them in a religious context. She is biased towards Joseph Smith, but I think that's a wise route to take to be sure you're not getting someone who's on the other side, maybe telling lies.
- Dr. Jessie Embry is a wonderful source on both African Americans' being denied the Priesthood, and Polygamy after Joseph Smith. She is also very active in the Church and uses a religious context for things while mostly giving the facts. I write "mostly" because I recently read a book she wrote where she avoided identifying Joseph Smith as marrying both a mother and her daughter.
- Dr. Todd Compton is also an active member of the LDS Church. He seems to me like a very balanced source - his thesis for In Sacred Loneliness was that polygamy was the new and everlasting covenant, but that it just didn't work in a practical sense. I feel like he really states the facts plainly, uses original sources as much as possible, gives balanced interpretations of events, etc.
- B. H. Roberts was an apostle who had some questions about the Book of Mormon and took a very direct approach at studying it. I have found him to be an excellent source for discussion, although becoming somewhat dated.
- I have also found the PBS documentary on the Church to be a balanced source. I feel that it shows the modern church for the good that it does, while also asking questions about its history and doctrine where appropriate. It uses interviews from both sides, as well as some in the middle ground.
Some LDS sources that are pretty negative toward Joseph Smith are Michael Quinn and Grant Palmer. They were LDS at the time of their publications (Quinn has since been excommunicated), but they sort of call the Church to repentance. You may want to avoid them for that reason, or may want to check them out to hear that side.
There's a difference between anti-Mormon literature and literature that doesn't put the Church in the perfect light. "Anti" material may ignore context or treat the Church and Joseph Smith as Satan's work, and so on. I did my best to avoid anything that put off that feeling. So I basically stuck with LDS authors or authors whose work was backed up by LDS authors, or authors whose work was not in direct regards to the Church, but had implication for LDS doctrine.
So in brief, it depends on what you specifically want to know about. My biggest question was obviously about polygamy, so I began with Compton, then Embry.
What is most important for anyone regarding these concerns is that you do not take my word for it. Check out as reliable sources as you can and then the decision is between you and your beliefs.