››  Jakob Nielsen, "Designing Web Usability" (New Riders, 2000. ISBN: 156205810X) - the usability bible

››  Steve Krug, "Don't Make Me Think" (Macmillan Computer Publishing, 2000. ISBN: 0789723107) - very easy read, straightforward - only about usability

Jeffrey Veen, "The Art and Science of Web Design" (New Riders, 2001. ISBN: 0789723700) - more indepth with design discussion as well as actual usability focus

Michael Drapin, Jon Lowy and Daniel Marovitz, "Three Clicks Away" (John Wiley and Sons, 2001. ISBN: 0471396826) - very good for e-commerce info