Free Kindle Books' Martin Luther PG E-Books:

Commentary on the Epistle to the Galatians

Concerning Christian Liberty

The Hymns of Martin Luther

Martin Luther's 95 Theses

Martin Luther's Large Catechism, translated by Bente and Dau

Martin Luther's Small Catechism, translated by R. Smith

An Open Letter on Translating

Selections from the Table Talk of Martin Luther

The Smalcald Articles

A Treatise on Good Works