Another common claim of your basic internet skeptic is that the gospels retroactively invented Jesus' prophecies to fit what later happened. In particular, the prophecy of the destruction of Jerusalem and of the Temple is a favorite target for such a claim. The prophecies are fairly specific about the Temple building being desecrated and ultimately completely leveled, the urgent need to flee when the time comes and the intensity of the suffering when the city comes under siege. Based on the very specific details of the prophecy that were fulfilled, skeptics naturally assume that it was retrofitted.
When I weigh this claim to see if it has any merit, I have to notice how often the gospels mention prophecies being fulfilled. I actually did a fairly in-depth study of that at one point. Luke is almost compulsive about it, once you put Luke and Acts side by side and consider them both. If he mentions a prophecy, he's going to mention the fulfillment if he's aware of it. He'll even go out of his way in the narrative to mention the fulfillment. I wonder if people these days have any idea what a big thing it was for the people of that day and that culture for Jerusalem to be sacked and the Temple leveled. It was their 9/11. I can't see any way that someone would record the prophecy of it at so much length, then not even mention the fulfillment of it.
The Gospel of John is a case in point. Nearly everyone agrees that it was written after the fall of Jerusalem (probably 25 years after, give or take a few years). It is the one gospel in the New Testament that doesn't go on and on about the prophecy of Jerusalem's upcoming destruction; it no longer mattered so much, twenty-five years after its fulfillment. When it is mentioned, it is lumped together with other things in the past. If someone wanted to retroactively invent a prophecy, the Gospel of John would have had all the opportunity in the world -- but it doesn't show much interest in the prophecy. It's old news.
The other three gospels go on at great length about the prophecy, but despite their track record (especially Luke's) of making a point to mention the fulfillment, there's no mention of the fulfillment here. None. After they make a point of recording prophecies and their fulfillment, and after basically whole chapters devoted to this particular prophecy, still no mention of the fulfillment.
I don't really buy that the prophecies were retroactively invented to point to a fulfillment. If that's the case, why in the world not mention it?
A note on the dating of the gospels: I would bet on Mark and Luke being written before the destruction of the Temple. This is based partly on a detailed study of how prophecies are used in each of the gospels, but also on the fact that Luke gives a play-by-play of certain figures in the early church -- and has it on his agenda to record early martyrdoms -- but suddenly stops in the early 60's A.D. without mentioning the martyrdoms of Peter or Paul. What are the odds that he'd stop where he did, given his agenda, if he knew of Peter's and Paul's martyrdoms? The most plausible explanation is that the narrative was up to then-current times when he stopped. Mark was a source for Luke, so Mark would have been completed before that. However, since we have evidence that Mark and Luke knew each other in person, it need not have been much earlier.
I would also bet on the first edition of Matthew -- the Hebrew/Aramaic one -- being written before the destruction. I have not found any details on when the translation and/or second edition of Matthew was written, but based on the deeply Jewish nature of that particular gospel and the non-mention of the destruction, I'd give decent odds that the main sayings of Jesus in Matthew were already in a set form (if still possibly in another language than the received text) before the destruction.