Gerard Serafin at Catholic Blog for Lovers posts a great list of converts and I added two in the comments:

Joseph Pearce: the author of Literary Converts, Old Thunder, Tolkien Man and Myth, and Wisdom and Innocence. He is the co-editor of the St. Austin Review and a writer in residence at Ave Maria.

Thomas Reeves: author of America's Bishop: The Life and Times of Fulton J. Sheen, A Question of Character A Life of John F. Kennedy, The Life and Times of Joseph McCarthy, and The Empty Church: The Suicide of Liberal Christianity