"DIVERSITY AND UNITY IN JUDAISM BEFORE JESUS" is a new essay, by Anthony J. Tomasino, on the Bible and Interpretation website. This is a very good introduction to the subject based on the literary evidence. Let me just add that, when you factor in ancient Jewish inscriptions (which I've been working on lately), the diversity becomes even more obvious and more wide ranging than suggested by the literary evidence alone. One important principle to keep in mind when studying ancient Judaism is that it was likely as varied then as it is today. There were fanatical Jews, devout Jews, reasonably religious Jews, nominally religious Jews, syncretistic Jews, Jews for Jesus, non-religious Jews, and former Jews back then as now. There were also gentiles (pagan and Christian) who had an interest in Judaism ranging from citing Jewish works in their histories to using Jewish ideas in their magic spells to visiting the synagogue regularly to converting and (for men) submitting to circumcision.
There! You just got a free summary of the section of Chapter One on which I'm currently working.