I saw Deer Hunter and All The President's Men on DVD recently and was struck by their relevance to issues being discussed today. Beyond explicit content is the Time Capsule effect: A glimpse of what people were thinking and feeling back then. It's a real refresher especially when discussing Vietnam.
Deer Hunter - Vietnam heroism and the steel industry
All the President's Men - No computers but journalistic standards (the lost art of sourcing a story) and a national capacity for shame
Others of interest might be
Nashville - Prescient on dirty politics
Network - Prescient on Media
Coming Home - Vietnam
Stay Hungry - early Schwartzenegger for laughs
China Syndrome - Nuclear
Norma Rae - unions
Apocolypse Now - Vietnam