Zend Framework in Action
By Rob Allen, Nick Lo, Steve Brown
Manning Press
ISBN: 1933988320

Pro PHP: Patterns, Frameworks, Testing and More
By Kevin McArthur
aPress
ISBN13: 978-1-59059-819-1
ISBN10: 1-59059-819-9

php|architect's Guide to Programming with Zend Framework
By Cal Evans
php|a Nanobooks
ISBN13: 978-0-9738621-5-7

The Definitive Guide to Zend Framework
By Zend
aPress
ISBN13: 978-1-4302-1035-1
ISBN10: 1-4302-1035-4

Practical Web 2.0 Applications with PHP
By Quentin Zervaas
aPress
ISBN13: 978-1-59059-906-8
ISBN10: 1-59059-906-3

Beginning Zend Framework
by Armando Padilla
aPress
ISBN-10: 1430218258
ISBN-13: 978-1430218258

Brazilian Books

Zend Framework Desenvolvendo em PHP 5 orientado a objetos com MVC
By Flávio Gomes da Silva Lisboa
Novatec
ISBN: 978-85-7522-158-7

Framewoks para desenvolvimento em PHP
Elton Luís Minetto
Novatec
ISBN: 978-85-7522-124-2

If anyone knows of any other books that discuss Zend Framework please reply to this post and I will add them to the list.