With Easter approaching, we'll be seeing a lot of discussion of what the New Testament says about Jesus' resurrection. It's often claimed that we don't have much, if anything, to go by other than the New Testament documents. But there's a lot of information about the resurrection, including some highly significant evidence for it, outside of the New Testament. I'll mention a couple of examples I've discussed before.
Some of the earliest extra-Biblical sources we have were contemporaries of the apostles, in some cases even eyewitnesses of at least one apostle. See here concerning Clement of Rome, here on Papias, and this article about Polycarp. Justin Martyr discusses Jewish corroboration of the empty tomb and seems to cite a Jewish source on the subject in the process. See here. Many other examples could be cited, like the ones I discuss here. The sources I'm citing wouldn't have been dependent on the New Testament alone for their information, and they sometimes tell us that they attained their knowledge by other means. Even where the resurrection isn't directly mentioned, it's often implied. When Irenaeus tells us that men like Clement and Polycarp and the apostolic churches corroborated the apostolic faith (Against Heresies, 3:3), for example, we know that the resurrection was part of that faith (e.g., 1:10:1-2). These sources corroborated scripture, but didn't get their information solely from scripture. Irenaeus writes, "Whatsoever things he [Polycarp] had heard from them [eyewitnesses of Jesus] respecting the Lord, both with regard to His miracles and His teaching, Polycarp having thus received information from the eye-witnesses of the Word of life, would recount them all in harmony with the Scriptures." (Fragments, 2)
Another source of information on the resurrection outside of the New Testament is the Shroud of Turin. I've discussed it in many previous posts. See, also, Dan Porter's blog and Barrie Schwortz's shroud.com, for example.
Notice that these lines of evidence are largely independent of one another. A case for the resurrection can be made from the New Testament without accepting the Shroud. Or an argument can be made from the patristic evidence that doesn't depend on the inerrancy of scripture or a high view of its historicity. Etc. Even a single one of these lines of evidence can be multi-layered. A high view of Paul's testimony doesn't depend on a high view of John's, nor is Polycarp's credibility dependent on that of Papias, for instance. Somebody like the apostle Paul not only offers his own testimony to the resurrection, but also gives us independent information about what others believed on the subject. Dismissing the fourth gospel as not coming from the apostle John still leaves us with what Paul reported about John's beliefs in Galatians 2 and 1 Corinthians 15 and what Polycarp attributed to John, for example.