Refactoring Databases: Evolutionary Database Design
Scott W. Ambler, Pramodkumar J. Sadalage
Addison Wesley Signature Series

If you know who Scott Ambler is, then you definitely want to read this latest book he wrote.  If you don't know who Scott Ambler is, you still want to read this book since it's most likely that you are dealing with databases at your job.

I haven't read it yet but just from the title and the cover description, it sounds like Scott has taken his Agile Modeling techniques to next step.  After all, Agile Modeling is all about starting from what you know and naturally evolving the database design as new design and architecture emerges.

Ron Jeffrey has a quick review of the book also.