Gods, Demons and Symbols of Ancient Mesopotamia is an exceptional resource to anyone interested in the religion and culture of ancient Mesopotamia. It is a thoroughly cross-referenced dictionary full of entries on everything from individual gods and goddesses like "Enki" or "Ishtar", to broad topics like "afterlife" or "divination". A brief but informative introduction lays out the broad periods of Mesopotamian culture, what is even meant by the geographical and cultural term "Mesopotamia", and which people constituted Mesopotamians at a given time. Most terms and names are rendered in Sumerian and Akkadian.
I've added it to my "perpetually reading" shelf because, as a reference work, I can see myself consulting it again and again as I read other historical or archaeological works about ancient Mesopotamia. I found this slender volume in the overstuffed shelves of Brattle Book Shop (a fabulous used bookstore in downtown Boston) and consider it a gem of a find. Even though it is a dictionary with discrete, alphabetically ordered entries, I read it cover to cover and was sorry to finish it.