One of the most fascinating stories I have come across on the internet is an interview with an Evangelical named "David" who attended the LDS Institute for four years while working on obtaining a PhD in Molecular Biology.
I'd like to share a portion of that interview with you (and I encourage you to read the entire interview at the link above) in which he discusses how Institute helped him see that Mormons really are Christians:
"How has your interaction changed your views of Mormons and Mormonism?
At the same time I started attending Institute classes, I made a point to read several books on Mormonism written from conservative evangelical perspectives or by individuals who had left the LDS Church. Those texts reinforced many of my early LDS preconceptions and argued adamantly that Mormons were not Christians. I believed as I read those books that I was preparing to enter a mission field, and during the first couple years of attending LDS classes and conversing with Mormons, proselytizing was always at the back of mind. I couldn't envision Mormons receiving an evangelical version of salvation without first accepting conventional Christian doctrine. My current perception of Mormonism is quite different. As I befriended more Mormons, I discovered that some of the most contentious issues that were the focus of anti-Mormon literature were simply irrelevant or ancillary to modern LDS beliefs and practices. The practical application of their faith and understanding in LDS doctrine was actually similar to that of other Christians with respect to purely biblical doctrine. Consequently, I no longer believe I am in a position to say the biblical salvation of Mormons is more in question than members of other Christian denominations. My current practice, which has contributed to the most productive and meaningful of my inter-faith relationships, is to treat Mormons as Christian brothers and sisters as opposed to members of a non-Christian cult.I was recently given a book by Stephen E. Robinson that makes several compelling arguments in favor of Mormons being Christians. I'm in agreement with him on many of his arguments, so I will limit the explanation of my change in heart and mind to one simple conclusion. To deny someone who accepts the atoning sacrifice of Jesus Christ the title of Christian is to deny the sufficiency of that sacrifice, as you surely can't be saved by grace through Christ and not be a Christian. I no longer argue, as I once did, that a precondition for that salvation is a proper understanding of its heavenly manifestation and the sufficiency of the grace that makes it possible. I still disagree with LDS doctrine as it pertains to grace, works and exaltation, but denying salvation to Mormons on those grounds requires passing judgment on the motive of their works. As a Christian and a witness to many apparently humble acts of Mormon service, I'm personally reluctant to pass judgment.Evangelical Christians sometimes acknowledge the promptings or the perceived presence of the Holy Spirit in their life, and I specifically remember attending a large LDS social event during the first year of my studies where I really felt the absence of the Holy Spirit. I never mentioned this feeling to any of my Mormon friends, but I share it now as an example of a subjective experience that I used to substantiate my academic rationale at the time for why Mormons should not be considered Christian. It's also relevant in that my current acceptance of Mormons as fellow Christians is the result of both intellectual argument and the accumulative effect of more recent subjective experiences. Shortly before my graduation from the LDS Institute, I was invited to attend a Mormon baptism, at which a moving testimony was given by the LDS friend of the woman being baptized. I could not have denied the profound influence of the Holy Spirit in that woman's life or in the lives of others who shared their testimony at an LDS church service I attended on a different occasion. The Spirit could also be felt in many of the prayers offered at Institute gatherings. Such spiritual fellowship is common amongst Christian brothers and sisters and I can't deny the significance of experiencing it amongst Mormons."
While David acknowledges that he still has doctrinal disagreements with the doctrines of the LDS Church, he at least sees that we are Christians.
David's statement that Mormons are Christians because "to deny someone who accepts the atoning sacrifice of Jesus Christ the title of Christian is to deny the sufficiency of that sacrifice, as you surely can't be saved by grace through Christ and not be a Christian" applies equally to all other denominations who accept the atoning sacrifice of Christ.
Christians will always have doctrinal disagreements with one another, but its time to put an end to the debate over who is a Christian and who isn't. No one except Christ is in a position to determine who is a Christian and who isn't.