Your guide for developing usable & useful websites from Usability.gov
http://www.usability.gov/guidelines/index.html

Guidelines

Throughout your Web design or redesign project, you should take advantage of what is already known about best practices for each step of the process. The Research-Based Web Design and Usability Guidelines, compiled through an extensive process of research and review, bring you those best practices.

Topics

The guidelines cover:

Usability Guidelines Book

The Research-Based Web Design & Usability Guidelines (PDF, 20.64MB ) includes all the guidelines, the Background and Methodology, the Glossary, Appendices, Sources, and the Author Index. We have included the document for your convenience but we are in the process of presenting the guidelines in a searchable database.

Limitations

The Guidelines may not be applicable to all audiences or contexts and are not fixed rules. Although considerable effort has been made to base the guidelines on research from a variety of fields, including cognitive psychology, computer science, human factors, technical communication, and usability; other disciplines may have valuable research that is not reflected in these guidelines.