There is no required text for this course; readings and notes will be given to you. I'll be releasing chapters of the course notes as we go. If you want to see last year's complete set of notes, please visit last year's course page.
If you like having a book for reference, an optional text is: Daniel Jurafsky and James H. Martin, Speech and Language Processing, 2nd edition, Prentice Hall, 2008. Draft chapters of the forthcoming 3rd edition are available online.