The Modern History Sourcebook:  The Reformation (Fordham University). 
The Protestant Reformation (AP European History) --> lots of good links. 
The Protestant Reformation --> primary source documents.
The Protestant and Catholic Reformations (Resources for Catholic Educators).
Timeline of the Protestant Reformation.
The Causes of the Reformation (Catholic Encyclopedia).
The Reformation Guide.
The Protestant Reformation (Catholic Encyclopedia).
The Protestant Reformation:  A Glossary of Terms (Queen's University, Belfast, No. Ireland).
A Study Outline of the Protestant and Counter-Reformations.
The Protestant Reformation:  A Review Sheet.
The 14th. to the 15th. Centuries:  The Church in Moral Crisis.
The Protestant Reformation: Early 1500s to 1600s --> a good overview.
Roman Catholicism and the Protestant Reformation (Britannica.com).
The Protestant Reformation in Europe.
The Reformation and Counter-Reformation --> a good summary article.
A Historical Summary of the Reformation Period.
Four Great Protestant Reformers:  Luther, Zwingli, Calvin, & Knox.
The Life of Martin Luther.
Martin Luther (Catholic Encyclopedia).
Luther's 95 Theses.
Wittenberg.
John Calvin (Catholic Encyclopedia).
Ulrich Zwingli (Catholic Encyclopedia).
The Catholic Reformation.
The Catholic Reformation (Western New England College).
St. Ignatius Loyola (Catholic Encyclopedia).
The Council of Trent.
The Council of Trent (Britannica.com).
Protestants and Roman Catholics.
Historical Overview of the Inquisition.
The Inquisition (Catholic Encyclopedia).