I wanted to send kudos over to Scott W. Ambler and Pramodkumar J. Sadalage for recently publishing a great book on the very topic of refactoring databases.
Refactoring Databases: Evolutionary Database Design
I'm a big fan of this book. You'll even find me saying so in the book's foreword :) Scott and Pramod have put together an authoritative source on refactoring databases much in the same style as Martin Fowler's original refactoring book. The book educates you on exactly what is database refactoring and a process for actually going about it. Most importantly, it provides an in-depth catalog of many different database refactorings, describing in detail exactly how to execute on them. Prior to this book, database refactoring was often just an academic exericse. But I hope now people will start to adopt this technique as a highly productive aspect of their agile database development.
And once again, Team Edition for Database Professionals hopes to help you realize the power of this technique by offering automated tooling around database refactoring.