Evelyn Underhill was one of the great Anglican thinkers of the first half of the 20th century, a group that includes Dorothy Sayers, C.S. Lewis and G.K. Chesterton (before his conversion to Rome). Her book "The Spiritual Life" was originally part of a series of broadcasts made prior to World War II. She published them in book form, in order to "present some of the great truths concerning man's spiritual life in simple language." She thoroughly and eloquently achieves her goal.
The present edition is an attractive reprint by Morehouse Publishing, and is part of its "Continuum Imprint" series, a series of reprints of great Anglican classics.
I used Underhill's "The Spiritual Life" as the text of our 2006 Parish Retreat, and although it was a challenging read (definitely 'steak' as opposed to 'hot dogs'), it was very well recieved.
One of my favorite quotes from the book is as follows: "We mostly spend our lives conjugating three verbs: to Want, to Have, and to Do. Craving, clutching, and fussing, on the material, political, social, emotional, intellectual--even on the religious--plane, we are kept in perpetual unrest: forgetting that none of these verbs have any ultimate significance, except so far as they are transcended by and included in, the fundamental verb, to Be: and that Being, not wanting, having and doing, is the essence of a spiritual life."