Getting Real (37 Signals)
First of all, this book is free. You can read it online here.
I love it because it contains a quintessence of right/proper/correct/efficient approaches to web development in modern environment.
In brief, it is a collection of small articles about all sides of software development, that can turn your idea of web development upside down. Especially in the extremes, if you are an independent freelancer or work for a big company.
It’s really worth reading. Even if you do not develop web apps.