In honor of Reformation Day, here are a few resources you might want to check out. Ligonier Ministries has made a number of Reformation-related e-books and audio/video resources available to download for free (until 11:59 pm, Oct 31, 2014).
Over on Amazon, several books by Martin Luther are currently free in electronic format.
Works of Martin Luther, vol. 1 (contains his 95 Theses)
Bondage of the Will (abridged ed.)