Designing Web Usability by Jakob Nielsen
These are bibles for anyone who wants to understand best practice for creating a Website consumers actually want to use. Neilsen’s brand-new one, Prioritizing Web Usability, was written with Hoa Loranger.
If you're new to web usability, this is a great book to start with. It's a fun, easy read that gives you a solid overview on designing clear navigation and intuitive online experiences. It's fast, funny and informative.
Great article on sidebars and web site usability. Explains why and how it should be done and also includes some added benefits for potential advertising options.