Excellent summary of philosophy throughout recorded history that hits all the major schools (Stoicism, Kant, Nietzsche, Heidegger, etc.) and explains them in a concise, digestible manner without dumbing things down excessively.
History of Western Philosophy by Bertrand Russell. Including the work of ancient thinkers such as Socrates, Plato, and Aristotle, as well as modern geniuses such as Descartes, Kant, and Marx, this book chronicles the entire span of philosophy in the Western world. It also includes intimate chapters regarding the philosophers with whom Lord Russell himself is most closely associated--Cantor, Frege, and Whitehead, coauthor with Russell of the monumental Principia Mathematica.