Logos, you're falling behind. Please bring these books out in Logos format. They are already in Kindle format, and I don't want to be tempted to spend money on Amazon.com. These are among the texts for a course on Readings in Modern Protestant Thought that is taught at Regent College.
David Hume, Dialogues Concerning Natural Religion
Friedrich Schleiermacher, On Religion: Speeches to Its Cultured Despisers
Georg F. W. Hegel, The Philosophy of History
Ludwig Feuerbach, The Essence of Christianity
Soren Kierkegaard, The Sickness Unto Death
Adolf von Harnack, What is Christianity?
Rudolf Bultmann, New Testament & Mythology