Not only is Christ Himself mentioned in extra-Biblical sources, but other facts are referenced, as well.

Josephus

Josephus was a Pharisee and a priest, born in AD 37, and considered today to be a reliable historian. (Strobel, 77-78)

He convened a meeting of the Sanhedrin and brought before them a man named James, the borther of Jesus, who was called the Christ, and certain others. He accused them of having transgressed the law and delivered them up to be stoned.

Josephus, The Antiquities

Tacitus

Tacitus was another trusted historian. Here, he speaks of Christ's death, Christians, and persecutions. Some also believe that the reference to the "checking" of the "superstition" by the death of Christ, and its following "break out," is an unknowing testimony to the response of the people to the resurrection of Christ. (Strobel 82)

Nero fastened the guilt and inflicted the most exquisite tortures on a class hated for their abominations, called Christians by the populace. Christus, form whom the name had its origin, suffered the extreme penalty during the reign of Tiberius at the hands of one of our procurators, Pontius Pilatus, and a most mischievous superstition, thus checked for the moment, again broke out not only in Judea, the first source of the evil, but even in Rome.... Accordingly, an arrest was first made of all who pleaded guilty: then, upon their information, an immense multitude was convicted, not so much of the crime of firing the city, as of hatred against mankind.

Tacitus, Annals 15.44

Pliny the Younger

Pliny the Younger was governor of Bithynia in northwest Turkey, son of the famous encyclopedist Pliny the Elder. In one of many preserved letters he wrote to Emperor Trajan, authored in about AD 111, he talks about the rapid and vast spread of Christianity. He also notes that the Christians were singing hymns to Christ as to a god, and that they were adamant in their beliefs, refusing to be swayed. (Strobel 83-84)

The Crucifixion Darkness and Earthquake

The Gospels record a darkness that covered the land at the time of the crucifixion, as well as an earthquake:

45 Now from noon until three, darkness came over all the land.

...

51 Just then the temple curtain was torn in two, from top to bottom. The earth shook and the rocks were split apart.

...

54 Now when the centurion and those with him who were guarding Jesus saw the earthquake and what took place, they were extremely terrified and said, "Truly this one was God's Son!"

Matthew 27:45-54 (NET)

33 Now when it was noon, darkness came over the whole land until three in the afternoon.

...

38 And the temple curtain was torn in two, from top to bottom.
39 Now when the centurion, who stood in front of him, saw how he died, he said, "Truly this man was God's Son!"

Mark 15:33-39 (NET)

44 It was now about noon, and darkness came over the whole land until three in the afternoon,
45 because the sun's light failed. The temple curtain was torn in two. 46 Then Jesus, calling out with a loud voice, said, "Father, into your hands I commit my spirit!" And after he said this he breathed his last.
47 Now when the centurion saw what had happened, he praised God and said, "Certainly this man was innocent!"

Luke 23:44-47 (NET)

Thallus had written a history in AD 52, which was quoted by Julius Africanus in about AD 221. Thallus talks about the darkness that covered the land, and tries to explain it away by attributing it to an eclipse--an impossibility given the timing of the crucifixion. (Strobel, 84-85)

Phlegon, a Greek author, recorded that in the fourth year of the 202nd Olympiad (AD 33), there was a great eclipse of the sun so that it became night during the day, so much so that even the stars could be seen. He also wrote that there was a great earthquake.

The Facts from the Extra-Biblical Sources

Even without the Gospels, we could glean quite a bit of information from these historical, extra-Biblical sources by themselves. We would know that 1) Jesus was a Jewish teacher, 2) many people believed be performed miracles and exorcisms, 3) some believed He was the Messiah, 4) the Jewish leaders rejected Him, 5) He was crucified under Pontius Pilate during Tiberius' reign, 6) though He died, His followers believed He was alive and were spread across a vast geography and demograhpic no later than the mid AD 60s, and 7) He was worshipped as God. (Strobel, 87)