Christianities and Judaisms (late to the game i know)
Charlesworth, OT Pseudipigrapha volume 1, xxix, has some nice quotes about diversity and unity. In my mind I'd agree with him (though apply it at least as much to 1c Xianity more than to Judaism): there needs to be more discussion on what early Xianity had in common at present, as the 'diversity' angle has really exploded. It tends to mask what folks had in common, while a better model theologically (i.e., categorization) and sociologically (i.e., conflict, etc) is to chart out what, say, Matthew and Paul had in common, before getting into their differences.
I saw someone engaging with Ehrman's book (not Misquoting Jesus) recently, with some great quotes on this issue. Anyone know who/where this was?