JOEL - Technically speaking, any church that "professes a belief in the teachings of Jesus Christ" as it states in the dictionary, must by definition be called Christian. However, the word Christian can also be used in a sectarian sense to mean belief in Christ according to a particular denominational view. In this case, those who claim that Mormons are not Christians are merely saying, Latter-day Saints don't agree with their definition of a Christian.

The controversy arises when one examines how a particular organization interprets and puts into practice the teachings of Christ and how Jesus Christ himself is defined by that religion.
People of different beliefs have their own ideas and interpretations of what a Christian is, based on what they have been told or what they have learned on their own. Everyone has had different experiences in life; everyone has their own unique personality. All these things influence our answer to the question of who is and is not a Christian. This influence affects how we interpret the Bible as well. It can cause two people to get two different impressions when reading the exact same scripture. Those with a judgmental attitude then take the stance that anyone that does not agree with their definition of Christ is non-Christian because they believe in a "different Jesus". Those who claim that Mormonism is not-Christian usually base their claim on a set of standards they find in the Bible. But with the many ways that people interpret the Bible, how strict can we be on the details? Can their be any deviance at all? How much deviance, if any, is allowed before one ceases to be a Christian?

Those claiming that Mormons are not Christians are sometimes reacting out of fear and a lack of understanding of what we really believe. And they exhibit a lack of confidence in what they believe by lashing out at Mormons. Obert Tanner said, "Only the confident can afford to be calm and kindly; only the fearful must defame and exclude."

Former President Jimmy Carter displayed a true Christian character when he told reporters that he not only considers Mormons to be Christian, but also believes his church is becoming too much like "Pharisees" in determining who is acceptable: "When questioned by the Deseret News about the Southern Baptist characterization of Mormons as non-Christians, Carter said his church's leadership has become 'narrow in their definition of what is a proper Christian or certainly even a proper Baptist.'" Carter is also quoted as saying, "I think that the worst thing that we can do, among the worst things we can do, as believers in Christ, is to spend our time condemning others, who profess faith in Christ."

Those who feel they must speak up against us should first consider the council found in Acts. The Apostles had been brought before a council that was deciding whether or not to slay them for what they were preaching. A wise member of the council stood up and said;

Acts 5:38
And now I say unto you, Refrain from these men, and let them alone: for if this counsel or this work be of men, it will come to nought:
Acts 5:39
But if it be of God, ye cannot overthrow it; lest haply ye be found even to fight against God.

Other Christians should also consider what Christ said about others who were doing things in His name but were not within His immediate group of followers:

"And John answered and said, Master, we saw one casting out devils in thy name; and we forbad him, because he followeth not with us.
And Jesus said unto him, Forbid him not: for he that is not against us is for us." (Luke 9:49-50)

His point is that we should not condemn others(eg. Mormons) who are at least trying to do what is right in His name.
But then critics will usually quote the scripture that tells them to "contend for the faith" (Jude 1:3)
However, the scripture says "contend FOR the faith" not "contend against other faiths". It's OK to proclaim and teach the Gospel as you believe it, but to defame and ridicule another faith is simply not keeping in harmony with the kind of love Christ showed for everyone.
Members of traditional Christian denominations think of themselves as sharing a core theology that links them and distinguishes them from other groups. However, this core theology rests on the dubious proposition that all present differences between Christian denominations are over purely secondary or even trivial matters that are not central to Christian faith. This view is very difficult to defend in the light of Christian history, back at a time when Protestants and Catholics considered such trivial matters as very serious differences

Many of those from traditional denominations suspect that Mormons are trying to downplay important theological differences between historical Christianity and Mormonism, in order to appeal to potential converts.
They interpret Mormon attempts to label themselves "Christian" as attempts to include themselves among the traditional denominations. In reality, however, the LDS Church does not at all downplay the big differences. In fact we openly discuss our beliefs in key doctrines such as the nature of God, the Atonement, baptism, salvation by grace, etc..
President Hinckley himself has often publically acknowledged this:
"...there are some of other faiths who do not regard us as Christians. That is not important. How we regard ourselves is what is important. We acknowledge without hesitation that there are differences between us." (LDS Conf. April1998)
Missionaries of the Church also discuss these differences during conversations with those who are investigating the Church.

In reality, the only one qualified to properly define the word Christian is Christ himself. No one on this planet has the perfect definition. Because of this, no one has the right or authority to pass judgement on anyone else and call them non-Christian, except maybe for Christ Himself.
As the Christian writer C.S. Lewis once said:
"It is not for us to say who, in the deepest sense, is or is not close to the spirit of Christ. We do not see into men's hearts. We cannot judge, and are indeed forbidden to judge. It would be wicked arrogance for us to say that a man is, or is not, a Christian in this refined sense." (Mere Christianity, Touchstone, 1996, pp. 10-11.)

The LDS people do not consider themselves as "traditional" Christians according to the modern day beliefs of all other organizations who profess a belief in Christ. The LDS church does claim to be Christian, however, because its entire existence is based on the gospel and life of Jesus Christ as they have come to learn it. Members learn about Christ, accept all His teachings, follow His example and dedicate their lives in serving Him. President Hinckley said, "Church members as a people are bound (together) by a common love for our Master, who is the Son of God, the Redeemer of the world. We are a covenant people who have taken upon ourselves His holy name."

Church Apostle, Boyd K. Packer said, "Every prayer we offer is in His name. Every ordinance performed is in His name. Every baptism, confirmation, blessing, ordination, every sermon, every testimony is concluded with the invocation of His sacred name. It is in His name that that we heal the sick and perform other miracles of which we do not, cannot, speak. "

One of the reasons why Mormons believe so strongly in their definition of the word Christian is because they believe so strongly in modern day revelation through our prophets. They believe Joseph Smith actually saw and communicated with God and Jesus and found out from the source the definition of a Christian. However, if people of other faiths also profess a belief in Christ and truly believe they are following His teachings, and conduct themselves accordingly, then they have every right to call themselves Christians as well. We just have to agree that we are all Christians in the spiritual sense of the word but that we might disagree on some of the doctrinal details.
Some excellent articles about how Mormons are Christians are at this site