Designing Interfaces by Jennifer Tidwell is a great reference text of common user interface design patterns for both web and desktop application designers.
Each pattern is broken down into the “why, when, and how” to use each pattern.
While it might seem obvious when it’s best to use something like a drop down menu, that isn’t always the case with complicated layouts. And for those with little experience in design and usability, Designing Interfaces is a gentle and complete introduction to the field.
