Data Modeling and Database Design

Data Modeling for Information Professionals by Bob Schmidt (ISBN: 0-13-080450-9) gets into much more than just data modeling, but the content is great.

The Data Modeling Handbook by Michael Reingruber and William Gregory (ISBN: 0-471-05290-6) gets a lot more into the data modeling design process.

Handbook of Relational Database Design by Candace Fleming and Barbara von Halle (ISBN: 0-201-11434-8) has full coverage of design methodologies .