Ebook: Code Quality: The Open Source Perspective

The book is full of hard-won experience cast nicely into prose. It's a very worthwhile read. The author doesn't shy away from explaining difficult or intricate concepts, where necessary, and each point is illustrated with example code from real systems.

For example, the chapter on Maintainability opens with four attributes of a maintainable system (from ISO/IEC 9126-1:2001) that really struck a chord with me.

Analysability: Finding the location of an error or the part of the software that must be analysed
Changeability: Implementing the maintenance change on the system's code
Stability: Not breaking anything through the change
Testability: Validating the software after the change

I know maintainable code when I see it -- it has a certain feel... Up until now though I've often struggled to express that feeling to non-programmers, or perhaps more importantly, to less experienced colleagues.

Highly recommended.