You can get a used set of the Great Books of the Western World for around $300.

You can get a used set of the Gateway to the Great Books of the Western World for around $50.

The Wikipedia articles for Great Books, Great Books of the Western World, and Gateway to the Great Books of the Western World are very complete.

Other Books:

How to Read a Book: The Classic Guide to Intelligent Reading by Mortimer J Adler and Charles Van Doren. 1972

Great Books: My Adventures with Homer, Rousseau, Woolf and other Indestructible Writers of the Western World by David Denby. 2005

The Western Cannon: The Books and School of the Ages by Harold Bloom. 1994

Genius: A Mosaic of One Hundred Exemplary Creative Minds by Harold Bloom. 2002

The Know-It-All: One Man’s Humble Quest to Become the Smartest Person in the World by A J Jacobs. 2004