One of these is Alexis de Tocqueville's Democracy in America. This book should be required reading for all Americans, whether in high school, college, or whenever. Everyone should have a copy of this on his bookshelf. Writing in the 19th century, Tocqueville presents a vivid description of how our democracy functions, how it formed, and its strengths and weaknesses. Tocqueville's style is remarkably clear and straightforward, well within the comprehension of high school students.
This book is a revelation to me, because I can see just how far our government has strayed from its original conception. Many of the weaknesses of the republic that Tocqueville described have become prevalent, and the strengths have been eroded by well-meaning progressives. As more people look to the federal government to solve the problems of our society, they undermine the very freedom that they claim to espouse.
Read the Declaration of Independence to understand the principles of our democracy; read the constitution to understand its structure. Then read Tocqueville. You won't be disappointed.