I just finished reading historian Bart Ehrman's latest book, called "Did Jesus Exist? The Historical Argument For Jesus Of Nazareth". Though most of his recent books have argued against Christian beliefs, since Ehrman is admittedly an agnostic with atheistic leanings, this is one that I believe most Christians with an interest in the mythicism issue would enjoy.
I myself have recently published a book on the mythicism issue, but I'd say Ehrman's book makes a more persuasive case. While I am a Christian and admittedly biased in favor of Jesus, Ehrman has absolutely no reason to believe in a historical Jesus other than having been persuaded by the abundant historical evidence. Though I suppose the same goes for me in some sense, since I am a former atheist who was swayed by the evidence, though not just for Jesus' historicity (as Ehrman was) but for His resurrection and divinity as well.
Erhman does argue against a divine/resurrected Jesus in this book, which is no surprise, but he does an excellent job of showing how all evidence favors the historical existence of Jesus, and even shows that the crucifixion is a detail that early Christians could not possibly have made up. Surprising to me, he doesn't put much stock in the references by non-Christians like Josephus and Tacitus. While he agrees that these authors certainly wrote about Jesus of Nazareth (mythicists generally argue that their references were forged), he considers them too far removed from the events to be of much use. Surprisingly to me (again), he argues that the references in Christian writings, including (but not limited to) the Gospels, are the best evidence for a historical Jesus.
Ehrman talks about the methods historians use when considering whether a certain event or detail is true or false.
One method is "Contextual Credibility", which is a negative criteria, which means that while it can be used to determine whether something is false, it cannot be used to determine whether something is true. "Contextual Credibility" considers whether the event in question fits with the historical context.
The second method is "Multiple Attestation", which is a positive criteria. Basically, if an event appears in multiple independent accounts, then it's more likely to be true. However, this cannot be used to determine whether something is false. An event appearing in only one source isn't evidence that the event never happened.
The third method is the "Criterion of Dissimilarity", which is also a positive criteria. It essentially says that if a detail is one that is unlikely to have been fabricated by the authors, then it likely happened. For example, there's no reason the Gospel authors would have wanted their Messiah to come from a small, insignificant town like Nazareth. It was even considered a bit of an embarassment. Thus Jesus' coming from Nazareth passes this criteria, meaning He probably came from Nazareth.
Ehrman points out that the crucifixion does very well with all three criteria. It is known that Romans were crucifying trouble-makers at the time, and Jesus certainly would have been considered a trouble-maker, thus it passed "Contextual Credibility". As for "Multiple Attestation", the resurrection is mentioned in many independent sources. As for the "Criterion of Dissimilarity", the crucifixion was considered a humiliating death, and even Paul considered it a "stumbling block" that he had trouble getting past. It's not a detail that would have been made up, and thus the crucifixion passed this as well.
While mythicists dismiss the New Testament authors as being biased, Ehrman, while agreeing with there is such a bias, says that the bias alone does not even begin to explain how Jesus could have been wholly fabricated. While mythicists argue that the earliest existing references to Jesus come from writings decades after the events, Ehrman shows that the claims about Jesus date to the 30's AD, no more than a few years after the events. The conversion of Paul, who was originally skeptical of Christianity and even persecuted Christians, can be clearly shown to have happened prior to 35 AD, which would have been impossible if the Jesus stories had yet to be "invented".
He argues that Paul's writings alone clearly show that he knew people who had to have known Jesus personally, including Jesus' brother, James, and at least some of the apostles, and found them persuasive. Ehrman believes that some details of the story of Jesus has been shown to have expanded over time (for example, he argues that the earliest traditions say that Jesus became the "son of God" upon being resurrected, then later ones say it was when he was baptized, and then later ones say he was the "son of God" all along), however, he points out that all traditions, even the earliest, have a clearly historical Jesus at their core.
Mythicists argue that the Gospel of Mark is the only original source for the story of Jesus, and that all other sources just borrowed from Mark. Ehrman shows that this is not the case (not only is there much that is original in Luke and Matthew, John's Gospel shows no dependence on Mark at all, and we also have other unique sources in other early non-canonical writings, and even much of what is said about Jesus in the Book of Acts shows no dependency on any of the Gospels - not even Luke's Gospel, despite having the same author as Acts!)
He also points out that while early non-Christians leveled all sorts of arguments against Jesus, one argument that was never leveled against Jesus was that He didn't exist at all. In fact, it's not until the late 18th century that the idea came into being.
One point I find interesting is that he claims that since all of the traditions show a historical Jesus who was crucified at their core, this is strong evidence for a historical Jesus who was crucified. He dismisses the so-called "discrepancies" as pretty much irrelevant to the question of a historical Jesus, saying that they're only evidence against those things on which they disagree (I like to point out that the accounts of Julius Caesar's assassination have clear discrepancies, but this doesn't cause us to question whether Caesar was assassinated).
I would have to say that the same goes for the resurrection itself. It's part of all early traditions, and is vigorously defended by the early church. The exact same arguments skeptics level against the resurrection are also equally applicable to the crucifixion and general historicity of Jesus. Skeptics point out "discrepancies" in the resurrection accounts, but also point out "discrepancies" in the crucifixion accounts. Skeptics argue that the "resurrection" accounts come from decades later, by people who weren't actually witnesses to the resurrection, but these are the exact same sources from where we get the crucifixion accounts. So the accounts of Jesus' resurrection are no more or less problematic than the accounts of Jesus' crucifixion.
Now, most skeptics go on to argue that since crucifixion doesn't involve anything "supernatural", but resurrection obviously does, then we have good reason to believe that the crucifixion happened but the resurrection did not. While I would consider this reasonable for those who don't believe in miracles, this seems, to me, to be the only reasonable basis for believing in the crucifixion and not the resurrection. However, it only applies to those who don't believe that miracles are possible, which those who believe in a transcendent God do. This means that there is no "historical" basis for doubting the resurrection any more than there is for doubting the crucifixion. It's all a matter of what one personally believes is possible or not.
He does, in my opinion, make some errors, though. As has been pointed out elsewhere, he suggests that a picture of a rooster which was brought up by Acharya S was Acharya's own creation. It was actually a drawing from another source that she simply used, and never claimed she drew it herself.
Also, he points out that Christians claim the vast number of ancient copies of the Gospels makes them "trustworthy", and he disagrees, saying that while it confirms that they do likely reflect (for the most part) what was originally written, this says nothing about whether what was originally written was true or not. But I have yet to see any Christian argue that the vast number of copies makes them "true". When Christians say it makes them "trustworthy", they mean precisely what Ehrman agrees with, that they're trustworthy representations of what the authors originally wrote.
He also claims that Jesus' apocalyptic language means that he was foreseeing the end of the world within a generation or two of His time, seemingly ignoring the more likely possibility that He was using hyperbole to get His point across.
Similarly, he sees Jesus' occasional third-person use of "Son of Man" to mean that Jesus saw the Son of Man as someone other than Himself. However, it was actually quite common in those days for people to refer to themselves in the third person as a way of stressing their own importance. Julius Caesar tended to refer to himself in the third-person as well, but that doesn't mean he wasn't talking about himself.
Ehrman discusses in the book how, in the classes he teaches, he devotes very little time to "the other side", saying that there is no "the" other side, but many different sides to the issues involved. To respond to all of it couldn't be done in a 15-week course. The same, more or less, goes for this book. While he addresses common mythicist arguments, he really doesn't get into the pro-resurrection or pro-divinity arguments for Jesus, really just saying that historians need to look at what's likely, and miracles are automatically unlikely, which I'd say reflects his agnostic/atheistic bias as there are many historians who believe in Jesus' resurrection and divinity.
He points out that mythicists frequently reject evidence that doesn't fit their biases (for example, they believe that since Nazareth didn't exist in the 1st century, all references to Nazareth in the New Testament must have been forgeries added later, despite no evidence that they were). But Ehrman more or less does the same with the resurrection. Not that he believes the resurrection accounts were forged after the writings of the New Testament, but that he believes they must have been events that were made up sometime between the crucifixion and the writing of the New Testament texts.
It should be noted that all of the early Christian sources agree that Jesus was resurrected. While, obviously, anyone who is skeptical of miracles will be skeptical of this claim, to say that the historical evidence alone does NOT favor the resurrection is incorrect. It most certainly does. Thus anyone who goes where the evidence points, rather than dismissing evidence that disagrees with their preconceptions, would have to conclude that Jesus' resurrection is as much a historical fact as His crucifixion.