The leader of the Catholic Church in Bavaria in the 1930s-40s, Cardinal Faulhaber, was anti-Hitler. When the Nazis ordered that the Jews had to wear arm bands, Cardinal Faulhaber had embroidered yellow Star of David arm bands put on the all the statues of Christ, the Virgin Mary, St. Joseph, St. Anne, St. John the Baptist, in the whole archdiocese of Munich.
Faulhaber's books were banned, and in 1934 and 1938 attempts were made to assassinate him. He continued to say and do things that demonstrated resistance to the Nazis, for instance he encouraged choral singing of classics from Bach and Handel. Why was this important? Hear me out: because it was virtually the only that young German Christians exposed to, and could publically celebrate, Old Testament (Jewish) Scriptures.
Connecting the dots, I learned that several of the heroic White Rose group --- ultimately bneheaded for trying to organize resistance to the Nazis in wartime Munich--- had met each other singing about such subversive things as "God's promises to Abraham and his seed forever..."
There were some truly great and righteous Bishops in Germany during the Holocaust and leading up to it. Some of the greatest anti-Nazi resistance was led by them.
Also, Father Maximilen Kolbe from Poland who's now a saint, but his name escapes me. A great hero of the Western tradition. He's probably my personal favourite. His story is in the Book of Virtues by William Bennett, which is a great book to read to kids. I read it when it came out.
Also, check out the link. Some heroic Polish heroes and martyrs. And also some who survived.
http://www.holycross.edu/departments/history/vlapomar/hiatt/opponent.htm