Is there a book out there that's the de-facto standard for describing best practices, methodologies, and other helpful information on gathering requirements for software and database projects? What about that book makes it special?
Software Requirements and More About Software Requirements: Thorny Issues and Practical Advice provide a solid coverage of requirements engineering in a manner that's generally independent of the development methodology used on the project.
There is now a third edition of Software Requirements that has not only been revised, but covers a chunk of the material in More About Software Requirements.
Software Requirements covers requirements from the perspective of both the customer as well as the requirements analyst. It contains discussions of elicitation, analysis, specification, validation, and management. It also includes information about product vision and scope, risk management, various requirements tools, and provides sample documents for different requirement related activities.
More About Software Requirements begins with a brief overview of many of the topics covered in Software Requirements. However, the focus is sightly more on the more agile approaches than the previous book, discussing the on-site customer, use cases, and determining the appropriate types of documentation needed to capture requirements.
In my answer to a related question, I quoted the book:
Managing Information Technology Projects: Applying Project Management Strategies to Software, Hardware, and Integration Initiatives by James Taylor, ISBN: 0814408117.
It is quite easy to read, IMO, and provides enough information about the requirements.
You also can read the chapter 11 of:
Project Management: A Systems Approach to Planning, Scheduling, and Controlling by Harold Kerzner, ISBN: 0471225770.
But it's not very detailed about the requirements, so I wouldn't recommend this as the only source or for people who are really interested in the subject.
Finally, you can read the chapter 3 of:
Advanced Project Management: A Complete Guide to the Key Processes, Models and Techniques by Alan D. Orr, ISBN: 0749440945.
It's much more detailed and explains requirements gathering, control systems, change control, etc.
I would also recommend Mastering the Requirements Process by Suzanne Robertson.
It gives a thorough description of all stages and criteria of the process.