The NLTK book, Natural Language Processing with Python, went on sale yesterday:
"This book is here to help you get your job done." I love that line (from the preface). It captures the spirit of the book. Right from the start, readers/users get to do advanced things with large corpora, including information-rich visualizations and sophisticated theory implementation. If you've started to see that your research would benefit from some computational power, but you have limited (or no) programming experience, don't despair — install NLTK and its data sets (it's a snap), then work through this book.
I want to be careful to distinguish Natural Language Processing with Python from the Natural Language Toolkit. The book has pedagogical aims, and NLTK is its technological centerpiece and main testing ground. However, NLTK is for advanced researchers as well. It is a scientific programming library, akin to SciPy, Octave, Praat, and R (and their for-profit counterparts). It provides lots of high-level functions for doing advanced things with linguistic data and theory. Slurp up a bunch of novels and explore their lexical statistics; traverse the WordNet; annotate your own data; prove logical theorems; and so forth.
By the way, the colophon explains that the whale on the cover is "a right whale, the rarest of all large whales", and that such whales "are not sexually mature until 10 years of age", which is, according to Steven Bird, the time from this book's birth (at Penn) to its publication. Many thanks to everyone who has contributed to the book and to NLTK!