First, there is no contemporary evidence what so ever. Not a single shred of documentation exists written in the time frame that mentions this person. Not a single Roman document ordering his death and not a single mention from any historian writing at the time, and 1st century Judea is a very well documented area where we have descriptions of multiple low level preachers claiming to be a messiah. The biographers of Herod never once mention him slaughtering children and the biographers of Pilate never mention him allowing a mob to grant immunity to a barbaric zealot while condemning Jesus, an act that was unprecedented in ancient times.
Second, even the Gospel accounts are demonstrably incompatible and historically inaccurate. In Matthew, Jesus is born during the reign of Herod, who died in 4 BCE, but in Luke, he is born during the Census of Quirinis, which occurred during 4-5 CE. One of those has to be wrong, so we cannot accept either as true. Beyond that, the simple removal of Jesus from the cross is historically inaccurate. Roman crucifiction was used as much as a warning to others as a punishment to the condemned. As such, bodies were not removed from the cross. They were left there to rot as a warning to others to keep in line. There is no way, the Roman authorities would have allowed the condemned to be removed from the cross on the same day of his execution. I know the Bible works in a cover about the bodies needing to be down before Passover, but the Romans wouldn't have done it.
Third, the earliest writings of Jesus we have come from Saul/Paul, a person who admittedly never met Jesus, and who's writings never actually refer to Jesus as an actual person who once walked the Earth, they are written to depict Jesus as someone who only existed in the Spirit World.
Fourth, the Gospels were all written at least 40 years after Jesus' death, so they provide no useful first hand information. We also have no idea who the actual authors were, so we cannot verify anything. Also, the earliest known copies of Mark (the first gospel written) don't even mention the resurrection, that wasn't added until later, which brings into question the whole resurrection story. Since the other 3 Gospels are mostly just copied from Mark (with some changes and embellishment) they are just as flawed.
Lastly, the "proofs" that Christians trot of ancient writings about Jesus have been mostly proven to be forgeries (see Josephus).
Stolen from http://www.reddit.com/r/atheism/comments/gj4a5/a_question_from_a_christian/c1nwhdw but accurate.