Ah, OK, well in that case, again John recommends this line for Black in his book.  Bogdan Lalic's more recent "Classical Nimzo-Indian" of course also covers these lines and, although it aims to be comprehensive in its coverage, is written slightly from White's point of view.

But to be honest, you can do worse than just use the e-book and ChessPub.exe right here (and they don't pay me to say this!!). John doesn't seem to me to be in the business of holding anything back, and is up front about where he thinks the conclusions he draws in his book are now being brought into question, so you are getting a really good up-to-date survey of these lines!  8)

For example, John covers the line 4.Qc2 0-0 5.e4!? in his book, but I think he would be the first to acknowledge that there have been many developments since then, and even since Lalic's book.  Not least, Karpov using it with White recently ...

Well, not sure if I qualify as an expert, but I think Carsten Hansen's "Nimzo-Indian 4.e3" is very good imho, and our own John Emms also covers 4.e3 b6 in his Black repertoire book "Easy Guide to the Nimzo-Indian".

I have not seen the recent book by Angus Dunnington "Nimzo-Indian Rubinstein", but I gather it is more geared towards explanatory text than theory, and given that it attempts to cover everything after 4.e3, it may be a bit lightweight for looking deeply at a specific variation.

As for the Classical Nimzo, it is quite rare for black to meet this with 4...b6 as White can simply play 5.e4, when Black has a very poor version of the English Defence (the black knight stops him playing ...f5!).