I worked a lot with Exchange 2007 in the last year. I designed, implemented and trained users.
Exchange 2007 SP1 starts a new wave of migrations. Time to certificate and improve knowledge!
When Exchange 2007 was release last year and I worked for InfoGroup Sistemas in Spain, I studied Exchange 2007 in detail. Below you will found my favorite books.
I teach these Exchange 2007 MOCs:
MOC 5047: Introduction to Installing and Managing Microsoft Exchange Server 2007.
MOC 5049: Managing Messaging Security using Microsoft Exchange Server 2007.
MOC 5050: Recovering Messaging Servers and Databases using Microsoft Exchange Server 2007.
MOC 5051: Monitoring and Troubleshooting Microsoft Exchange Server 2007.
Microsoft Exchange Server 2007: Tony Redmond's Guide to Successful Implementation
Probably the best book about Exchange 2007 around. Amazon
How to Cheat at Configuring Exchange Server 2007: Including Outlook Web, Mobile, and Voice Access
Henrik Walther is Microsoft Exchange MVP (Most Valuable Professional) and writes Exchange-related articles for http://www.msexchange.org/, one of the best sites of Exchange Server. Great book, very easy to read and full of examples. Amazon
MCTS Self-Paced Training Kit (Exam 70-236): Configuring Microsoft Exchange Server 2007
This MS Press book is not good like others Training Kit I read before. But will help you to understand the exam. Amazon