One of the first requirements for anyone considering building or operating a website should be Steve Krug's miraculous book - Don't Make Me Think. This short, 3-hour read has been next to my desk since I bought it and I doubt it will ever move. Mr. Krug's simple ingenuity and intuitive reasoning are why I work so hard to design with usability in mind.

A good thread at HighRankings discusses Mr. Krug's efforts and his recent interview with Management Consulting News, which sadly was not representative of his extraordinary insight and perception - either that or he's a much better writer then he is an interviewee. Also, if you have the budget, consider hiring Krug; I can say with certainty it will probably be the best website investment you make.