I just saw on Twitter that a free e-book is now available from Ascension Press to combat lies and inaccuracies in Angels & Demons:
Angels & Demons is a thinly-veiled, but brutal attack on the Catholic Faith that will again shake the faith of potentially millions of people who know little about Catholic teaching and Catholic and Western history. It is full of half-truths, historical inaccuracies, and outright lies.
Answering Angels & Demons, by Mark Shea is an electronic book provided for free to help you answer the errors contained in the book and movie. Please feel free to download this resources and share it with your friends, family and neighbors.
Just go to http://answeringangelsanddemons.com/ to get it (PDF, 23 pages).