Are there Christian denominations debating whether Jesus was really the son of God?

Yes. Mine is--we recognize that Jesus can't be the son of god, because we recognize that an inescapable corollary of the Christ's teachings is that there is not a god. Thus, as Christians, we are enjoined from believing in a god, and so we recognize that Jesus can therefore not be its son.

I don't doubt that there are some denominations, especially ones with an affinity for Islam, that are actually debating whether Jesus was the son of God or not.

I had a discussion with a young Muslim woman about two months ago, where we were discussing our religious beliefs. She told me, "It's better that you don't believe Jesus was the son of God, or God will be angry with you when you die and go before him. He will say, why you believe Jesus was my son? I said in the Qu'ran that I cannot have a son, nor was I created."

I said, "hey it's a central tenet of the Christian faith" and left it at that.

Now there are some interesting nuances on this question. Jesus has been characterized as "beloved of God" or as one who "comes from God" in order to outreach to Muslims, who have a knee-jerk reaction when they hear that Jesus was the "Son of God." This to them is anathema.

I'm not so sure that these characterizations take too much from His divinity.

Socinian/Adoptionist churches:

• Christadelphians
• Christian Churches of God
• Christian Science
• Church of the Blessed Hope
• Spirit and Truth Fellowship
• The Way

Any doctrine teaching that Jesus is not literally the Son of God (or God the Son, if you will) would have to be classified in the all encompassing "Non-Trinitarian" category. Most non-trinitarian doctrines do teach that Jesus is the Son of God, but there are some which do not. The two main ones, which come to mind, are:

• Adoptionism - Teaches that Jesus did not become God's Son until God adopted him. Typically, Adoptionists believe that God adopted Jesus at His baptism.
• Sabellianism - Teaches that the Father, the Son, and the Holy Spirit are simply three different modes through which the same God has manifested himself to the world. It teaches that there are no separate persons within the Godhead.

Even among other non-trinitarian doctrines, which traditionally teach that Jesus is the literal Son of God, there may be a small number of adherents who may diverge on that point. For instance, even though Socinianism teaches that Jesus is the Son of God, the doctrine is conducive to those who might not believe it in a literal sense.

Although these doctrines have been believed, to varying degrees, throughout history, there is no mainstream support for any of them among any of the major Christian denominations. Even among the major non-trinitarian denominations, such as Jehovah's Witnesses and The Church of Jesus Christ of Latter-day Saints, Jesus is taught to be the Son of God.

I imagine, for instance, that you would be hard pressed to find a church, today, teaching Adoptionism doctrine. However, most of these doctrines did have some major supporters in the past, particularly in the early church and the Radical Reformation. Therefore, even though you may not be able to find a church who teaches these doctrines, you will be able to find a fair amount of literature about many them if you look hard enough.

Your question ends asking this:

"In other terms, is there a way to conceive Christianity refusing the concept that Jesus was the son of God?"

It would be a clear "NO".

To say that Jesus is just like any other great Godly man having special friendship with God, as you have put it in one of your comment, is to look at those places in Bible where Jesus is equalled with God, as major flaws and contradictions in the Bible. To take Jesus in this manner and to say that He was only human and with no divine nature is to reduce the whole Bible into a bundle of inconsistencies. All those verses in Bible where Jesus is sometime portrayed as human and sometime as Divine, remains in harmony with each other especially in New Testament, only when we accept Jesus as having both human as well as Divine nature. Without this we would be representing Christianity in complete contradiction to the Old Testament as well as what we have in New Testament.

We cannot overlook all those verses where Jesus is clearly portrayed as having Divine nature. He was crucified for saying that He was Son of God. Further in John 8:58 He declares:

John 8:58 Jesus said to them, “I tell you the solemn truth, before Abraham came into existence, I am!”

Then we have at other places where Jesus forgave third person’s sins. If you do something against me, I have the right to forgive you. However, if you do something against me and somebody else comes along and says, "I forgive you," what kind of cheek is that? The only person who can say that sort of thing is God himself, because sin, even if it is against other people, is first and foremost a defiance of God and his laws. So along comes Jesus and he says to sinners, "I forgive you." The Jews immediately recognize the blasphemy of this. They react by saying, "Who can forgive sins but God alone?" Not only did Jesus forgive sin, but he asserted that he himself was without sin. And certainly sinless-ness is an attribute of deity. as if it is against Him, equalling Himself as God and many places He equalled Himself with God. All these events and quotations would glaringly be biggest contradiction which would stare at Christianity and for which there would be no plausible explanation to offer.

In the verse below, we find Jesus giving the highest honour to John the Baptist and that John is more than a prophet.

Matt. 11:9-11 What did you go out to see? A prophet? Yes, I tell you, and more than a prophet. This is the one about whom it is written: ‘Look, I am sending my messenger ahead of you, who will prepare your way before you.’ “I tell you the truth, among those born of women, no one has arisen greater than John the Baptist. Yet the one who is least in the kingdom of heaven is greater than he is.

This would mean that Jesus makes Himself smaller than John, which cannot be. Since John was someone who was more than a prophet, it only shows that Jesus was not just a prophet or someone more than that but someone much greater than that.

Again we find in Gospel of Mathew;

Matt. 16:13-17 When Jesus came to the area of Caesarea Philippi, he asked his disciples, “Who do people say that the Son of Man is?” They answered, “Some say John the Baptist, others Elijah, and others Jeremiah or one of the prophets.” He said to them, “But who do you say that I am?” Simon Peter answered, “You are the Christ, the Son of the living God.” And Jesus answered him, “You are blessed, Simon son of Jonah, because flesh and blood did not reveal this to you, but my Father in heaven!

And finally: Early in the Old Testament God introduced this idea of one innocent being shedding its blood in place of the sinner’s. However the solution of sacrificing bulls and goats and lambs for the sins of each person’s sin was a temporary fix. The next year, another animal would have to be sacrificed for the same person. A more permanent solution was needed, as noted in Hebrews 10:4:

For it is impossible for the blood of bulls and goats to take away sins.

That meant a human was needed to die for humans’ sin. But all humans are sinful, so another sin-filled person dying for us just wouldn’t work. A human without sin was needed. But ever since Adam, every human born is sin-filled, so how could a sinless man happen? The only way was if God did it Himself.