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general
Richard Foster, Celebration of Discipline (especially chapter 1)
John Ortberg, The Life You've Always Wanted (especially chapters 1-3, 12)
Dallas Willard, The Spirit of the Disciplines (anything by Willard, really)
Sabbath
AJ Swoboda, Subversive Sabbath
Marva Dawn, Keeping the Sabbath Wholly
Eugene Peterson, Confessions of a Former Sabbath Breaker
Tim Keller, The Wisdom and Sabbath Rest