The comprehensive guide
This is the comprehensive guide to the MySQL 5.1 Cluster Certification. The book is well formatted, written, and provides lots of guidelines that are hard to pick up by just RTFM-ing the manuals. The book starts with a discussion of what is high availability and what is not that is great for those new to the subject. Then it gets very heavily into the NDB aspects of MySQL Cluster.
This is not a book for those wanting to start administering MySQL databases as it is very cluster specific. But many of the general topics would be of value to any DBA.