Gary Spruch of the American Jewish Committee based in New York wrote an insightful piece on Heschel's work with the Catholic Church prior to the Second Vatican Council. In the foreward, Rabbi Gary Greenbaum writes, "Although Heschel's role in this most important chapter in Catholic-Jewish relations is not well-known, it may well be here that his great moral voice, his deep theological thought, and his true love of humanity will have had their most lasting effect."
The Shalom Center in Philadelphia has compiled a magnificent list of articles by Rabbi Heschel and other wise Jewish voices about his impact and work. Well worth the trip if you're looking for new ways to think about the war, praying, or even environmentalism.
Rabbi Gerald Zelizer was at the Rabbinical Assembly meeting where Martin Luther King Jr. was greeted by the singing of "We Shall Overcome" in Hebrew. He writes about how King's speech that day impacted him.