Monographs aren't really a thing in NLP, beyond theses. There are a couple of reference books most people lean on, though:

* Foundations of Statistical Natural Language Processing by Manning and Schütze

* Speech and Language Processing by Jurafsky and Martin (which is being revised for a third edition, which you can look at: https://web.stanford.edu/~jurafsky/slp3/ )

Beyond that, you're basically stuck reading the research literature. On the up-side, most of that literature is freely available from the ACL anthology at http://aclweb.org/anthology/