100 Things Every Designer Needs to Know About People by Susan M. Weinschenk, PhD
100 Things Every Designer Needs to Know About People is a list of all the bits of psychology that they should be teaching in design school. It’s neatly organized, easy to refer to, and easily the best $30 I’ve spent on books in the last few years. If you’re even remotely interested in improving the effectiveness of your designs through an understanding of cognition, this is a great place to start.