Dictionary of Religions, the Penguin

This book contains a brief description of most of the major religions. What is helpful is that terms that one would not be familiar with unless one was a member of a particular religion are illuminated. So if you were reading about religions and wanted to know what a "Mo Tzu" was, then you could find that it is "an anti-Confucian, pragmatic philosopher" or if you read in the Bible about the "Sadducees", then you could find out that they were "a religious party in Judaism ... theologically conservative, rejection post-exilic angelology and demonology and the belief in bodily resurrection." With maps, an extensive Bibliography and a General Index, I find this book very useful. It is by no means comprehensive in every religious term but a great reference for obscure terms not found elsewhere.