A trick I like to pull on something like this is pick something that people think they know, and give them an entirely different spin on it, aiming for a "holy shit I never thought of that" reaction.
Alternative views on major historical events, and the practice of the media and the educational system to gloss over these possible variations in perception to give a "sanitized" view of history and world events. When and why does this occur, and is it justified? For example, the targeting of Japanese civilians in the Second World War which gave rise to the most deadly bombing raids in the history of the world even before atomic weapons came into play.
"Lying in the History Books" would be easy to run with, there's excellent resources on it pretty much anywhere you turn; did you know Christopher Columbus not only trafficked in slave labor and committed genocide, but also gave young native girls as sex slaves as gifts to his friends who came to the "new world"? This has an added bonus of being able to talk about war crimes committed by the United States which we've never been accosted for. And whether or not you're for Evolution, they've been using outdated and erroneous information in textbooks to back it up for decades (like the evolution of the horse argument).
The relationship between the current financial crisis and the oversimplification of political issues concerned in campaigns when it comes to advertising for your candidates. No candidate wants to be associated with raising taxes because lowering taxes is something that the American public is convinced - after countless campaigns - that it's something they can demand and require from any candidate. Also President Clinton's role in forcing financial institutions to invest in subprime mortgages, leading specifically to this chain of events. Is this all because political campaigns have been oversimplified and the American public is too "dumbed down" to grasp real political issues, forcing their elected officials to do idiotically dumb things to stay popular and stay in office?
Another one could be the rise of Islamic terrorist groups during the Cold War, many of which were supported by the United States. It's a little generic but it'd be good information for people to hear; you can talk about how we attempted to manipulate foreign governments in our conflict with the U.S.S.R. and how Israel has influenced our standing in the Middle East leading up to the First and Second Gulf Wars. I feel like I'm missing something interesting with this one, maybe see if China can be related and take a look at our relationship with the U.S.S.R. given our occupation of Japan and the Philippines leading up to the Vietnam War. That'd broaden the scope from the Middle East which is the topic most people would expect you to stick with. Plus, having the Vietnam War and the Second Gulf War in the same speech would be so much fun! You could show how different they are in comparison without even really comparing them.