Hammer’s German Grammar and Usage is the bible of German grammar books. As Amazon says, it is “the pre-eminent, most authoritative German grammar reference in the English language”. If you’re serious about German grammar, you need this book.

It can sometimes be hard to find exactly what you’re looking for due to the cross-referencing, but rest assured: any German grammar question you could possibly have is inside this book.
The examples are good and the writing is clear.

Author: Martin Durrell
Pages: 576
ISBN: 0071396543