Sue Bender , Plain and Simple: A Woman's Journey to the Amish, HarperCollins, 1989; ISBN 0062501860.
Examines the value of simplicity and clarity.
Leonard Coren , Wabi-Sabi: For Artists, Designers, Poets, and Philosophers, Stone Bridge Press, 1994; ISBN 1880656124.
Wabi-sabi is an aesthetic celebration of the rough and functional.
Richard Coyne , Designing Information Technology in the Postmodern Age: From Method to Metaphor, MIT Press, 1995; ISBN 0262032287.
Discusses the differences between modernist and postmodernist thought including an excellent discussion of the importance of metaphors.
Philip B. Crosby , Quality Is Free: The Art of Making Quality Certain, Mentor Books, 1992; ISBN 0451625854.
Breaks out of the zero-sum model of the four variablestime, scope, cost, and quality. You can't get software out the door faster by lowering quality. Instead, you get software out the door faster by raising quality.
George Lakoff and Mark Johnson , Philosophy in the Flesh: The Embodied Mind and Its Challenge to Western Thought, Basic Books, 1998; ISBN 0465056733.
More good discussion of metaphors and thinking. Also, the description of how metaphors blend together. The old software metaphors drawn from civil engineering, mathematics, and so on are slowly morphing into uniquely software engineering metaphors.
Bill Mollison and Rena Mia Slay , Introduction to Permaculture, Ten Speed Press, 1997; ISBN 0908228082.
High-intensity use in the Western world has generally been associated with exploitation and exhaustion. Permaculture is a thoughtful discipline of farming that aims for sustainable high-intensity use of the land through the synergistic effects of simple practices. This has some parallelism to XP. For example, most growth occurs at the interactions between elements. Permaculture maximizes interactions with spirals of interplantings and lakes with wildly irregular edges. XP maximizes interactions with on-site customers and pair programming.