A visual dictionary of art (New York Graphic Society)
Found at the "for free" pile in the laundry room. I had a lot of books about art history but never an art dictionary. I found almost every artist and styles I could think of. Of course, it lacks in information about contemporary art but hey! It was for free and it is still a helpful guidance for art history or further research of certain artists. Wikipedia might be faster and more up to date but I do enjoy this book and exploring random artists I've never heard of before.
This book also covers a great section about art from all over the world. Not just European Art and styles throughout art history, but also American Art, Chinese Art, Japanese Art, Korean Art, Islamic Art, Indian Art, South-East Asian Art, Pre-Columbian Art, North American Indian Art, African Art and Oceanic Art. This book is a great way to discover art and artist which are mostly unknown in our society.