The Intercollegiate Studies Institute has produced an excellent series of small books as student guides to the major disciplines:
"The ISI Guides to the Major Disciplines are reader-friendly introductions to the most important fields of knowledge in the liberal arts. Written by leading scholars for both students and the general public, they will be appreciated by anyone desiring a reliable and informative tour of important subject matter. Each title offers a historical overview of a particular discipline, explains the central ideas of its subject, and evaluates the works of thinkers whose ideas have shaped our world. Published guides assess the fields of literature, political philosophy, U.S. history, economics, psychology, and other areas."