Meister Eckhart: A Modern Translation by Meister Eckhart and translated by Raymond Bernard Blakney: https://www.goodreads.com/book/show/6885348-meister-eckhart

Other notable authors, titles, and subjects, some that others have already mentioned: Aldous Huxley, Hermann Hesse, Rainer Maria Rilke, Khalil Gibran, sufism, The Philokalia, etc.