Philipp Koehn
Statistical Machine Translation
The book is not yet released.
Christopher Manning and Hinrich Schütze
Foundations of Statistical Natural Language Processing.
Chapter 13 is on MT. The complete book is available online but requires login.
Daniel Jurafsky and James H. Martin
Speech and Language Processing (2nd Edition - 2008)
Chapter 25 (chapter 21 on first edition) is on MT. The revised Second Edition was released this year, and they claim this chapter was extensively rewritten.
W. John Hutchins
Introduction to Machine Translation
1992
Good for background and historical aspects of MT. The complete book is available online.