If you're responsible for designing anything, website or not, read this book. Now.

It's great at explaining why usability needs to be the primary concern in developing any sort of interface. The way a user looks at a site is very different than the way a designer does, and "Don't Make Me Think" points these things out clearly and easily.

Even the title is a lesson, one of the most important in the book; "Don't Make Me Think." If the interface makes the user think when they don't need to, it's bad. Cartoons, short chapters, and plenty of illustrations make this a quick, light read that will leave you convinced to spent more time on usability.

While the book's shortness is one of its strengths, I'd say it's also its only weakness. It convinces you to spend more time on usability, but doesn't go too much into how. But that's covered in many other books, and a few are even given at the end.