By far my top choice for a brief and understandable introduction to the academic study of religion. Includes chapters on the psychology of religion and the sociology of religion. Also covers several other topics.  

This is an introductory survey and practical hands-on guide to religious studies as both an inner experience and as a social phenomenon. A balanced discussion of intellectual, worship and sociological aspects of religion, the guide explores the symbols and rites of religion; the expression of religion through art forms; the ethical aspects of religion; and the conceptual messages of religion. An ideal introductory text to Theology, Philosophy, and Religion.