I believe itās kind of ironic in a way. The original protestant reformers, those that broke off from the Catholic church, Luther, Calvin, etc, pretty much didnāt contribute anything. It was only later on, many generations removed, when a lot of intelligent protestant theologians came on the scene that have been acknowledged by many to have contributed a lot. People like Karl Baarth, Paul Tillich, John Stott, Meredith Kline, Dietrich Bonhoffer, George McDonald are said by many to have contributed a lot.
But, for me, three protestant theologians that are very good are these:
N.T. Wright, very thoughtful bishop of the Church of England. Broke with traditional protestant views on Justification. His work on it is not exactly Catholic, but his real expertise is his study of the historicity of the Gospels and Jesus Resurrection from the dead. His knowledge of that is superb.
C.S. Lewis, a man who is loved by Christianās of all denominations. he was a great defender of the faith that explained the teachings of Christianity almost better than anybody. He also had a lot of Catholic type beliefs. He was a āhigh churchā Anglican.
William Lain Craig, not exactly theology, he is more like Philosophy and apologetics. None the less, Dr. Craig, a Baptist, is perhaps the best defender of Christianity today. He has revived the cosmological argument, and argues very well on multiple levels for the existence of God. His books are well worth a read.
Not to mention, Martin Luther King jr was a protestant also.