This biography of Just James, while fairly succinct, seems to cover most of the current research on the subject (at least through 2005). I was initially a bit skeptical of Butz's book, especially as in his preface, he pointed out how much he respects the work of Robert Eisenman, whose biography of James may qualify as one of the longest ever but is also one of the most kooky. But Butz doesn't quite try to tie James in with the Dead Sea Scrolls and make claims that the entire original Christrian movement was actually some kind of Essene movement revolved completely around Jesus's family and that it had only ever aimed at being some kind of worldly Jewish Messiah, though in some ways he comes close.
What I like about what Butz does is that he doesn't quite go so radically far. Rather, he tries to reclaim James and the early Christian movement as part of Judaism, and while he does fall into the common Protestant and often secular point of view that James and Paul were at cross-purposes, which colors many of the insights he manages to provide, he does still manage to show just how important James was to early Christians and how that early movement was signficantly Jewish in form and nature. (Plenty of newer works call into question the antinomial Paul who created some kind of new movement that had little in common with what Jesus actually taught.)
Some of the interesting insights include a correction of the common idea that James and the rest of Jesus's family did not support Jesus during his physical life—that is, that they were not convinced of his ministry until after his resurrection. Some of this interpretation comes from the way we have read certain scriptures out of context, and some has to do with how later generations want to portray Jesus. Butz argues, fairly convincingly, that the family probably had connections to Jesus's ministry well before his resurrection.
Butz also shows how James fit within Judaism, and while claims that James was a Pharisee seem a bit too far out to be believed to me, there is a case to be made that in many ways the early Christian movment had much in common with Pharisaism—and in that way, James, Paul, Jesus, and the whole lot would have been a kind of offshoot.
The book ends with a call to unite the Muslim, Jewish, and Christian faiths through a degree of compromise. It's not a strong ending to me, insofar as I don't think things like divinity of Jesus are really up for debate between the faiths. But the push to remind people of how Christainity started in Judaism is a worthy enterprise.