Don't Make Me Think

Steve Krug's nice thin "common sense approach to web usability".

Very practical book of good web site design techniques. Two things basically: follow conventions so user's easily know what to do with your site and rigorous but simple, easy and cheap testing. One of the points is that if the testing is not simple, easy and cheap it won't be rigorous because to be rigorous you need to do it early and often. Good points of no such thing as "average user" ect. Excellent read altogether.