You didn't mention the age of your students but I am assuming they are high school students.

How about Far Side cartoons by Gary Larson? There are other cartoonists that can be featured. Its a good way to open discussion regarding point of view and critique. Try this page:

http://www.cagle.com/teacher/

I'm not sure how far you can go in a Catholic school but its also a good way to approach subjects that may be controversial.