A wonderful introduction to natural language processing using the NLTK toolkit. This book also serves as an introduction to Python for those new to the language (and to programming, though the pace is pretty fast). And for those like me, not new to Python but totally ignorant of NLP, it contains a wealth of interesting material. Finally, the examples showcase the elegance of Python as a language for text processing.
I am taking down the git.krondo.com website and just keeping everything at github.