I believe Jesus Christ existed. However, since I'm a buddhist I don't believe in God (or at least not God as Christians define him) so I do not believe he was the son of God. I share my views of Christ with Tenzin Gyatso (14th Dalai Lama) and many other Buddhist scholars. He believed that Christ was a human being who was enlightened, but stayed on earth to dedicate his life to the welfare of other human beings (a bodhisattva), like Buddha. In fact, Buddha and Jesus have a lot in common. They both radically changed the way people thought about religion. Many of their teachings and analogies (though certainly not all) coincide. For example, Jesus emphasized non-violence, turning the other cheek as did Buddha. Jesus also lived simply and taught through parables as did Buddha. Jesus emphasized the need to be active in the world but to also be not of the world. Buddha taught the need for non-attachment. In short, I think Jesus showed a common humanity with important figures from other religions, but found his own expression of it.
However, I'm not saying Jesus was a buddhist or a Muslim. Those who see other religions in Jesus seek to find unity, to humanize traditions. Unity however for us humans can only come from an acceptance of, even a celebration of, differences as well as similarities, something Jesus was adamant about.
Although I think Jesus his original teachings remain valuable, they have been used for personal gain and subjected to random interpretation throughout the centuries. Also, severe misconduct of Jesus's teachings by important figures in the Christian religion (I think everyone knows what I'm talking about) has put his teachings in bad light.