Christopher D. Manning (–1965)

Along with Speech and Natural Language Processing by Jurafsky and Martin, this is the standard book on using probabilistic methods to analyze natural language. It has clear discussions of such core areas as N-gram language modeling, parsing, part of speech tagging, and information retrieval. The exceptionally lucid chapter on Hidden Markov Models is worth the price of the book alone. This is the best introductory textbook for newcomers and a useful reference for everyone else. Essential.

Good broad-based overview of information retrieval concepts

Although the required text for the class in statistical natural language processing, this was not as clear, particularly regarding algorithms, as "Speech and Language Processing" by Jurafsky and Martin.

A very good introduction to information retrieval by Manning et al.