Food, Inc.

See it and barf.
It doesn't really tell you something you don't know, but it does so cogently and convincingly.
That 1 in every 4 children now has diabetes. 1 in 2 or 3 if the child is poor.
That 3 or 4 companies control all the "food" we eat.
That farming has become hell for animals and humans.
That the "regulators" who work at the FDA are former lobbyists for the food industry.
That everything you eat and even stuff you don't has corn in it.
That a lot of what you eat has stuff it shouldn't have in it.
That the reason for the massive e-coli outbreaks is that cows are fed corn instead of grass.
That basically when we are eating beef, we are eating cow manure (I find the disclaimers of food companies to cook the meat to within an inch of charred, the height of cynicism. They are the ones who should not be providing us with extra ingredients like e-coli. It should not be our responsibility to kill those germs).
That those angelic companies like Tom's of Maine that you think are righteous are actually owned by Colgate, like Ben and Jerry's is owned by Unilever.
But I learned that the reason why junk food is cheap and broccoli isn't is because the government subsidizes corn and soybeans, but not other crops.
I also learned that all those Mexicans y'all hate so much are here working in subhuman conditions in meatpacking plants and other industrial hellholes because they used to be corn farmers back in Mexico who stopped making a living after NAFTA dumped cheap American corn on Mexico. I know that it is the workers that get arrested and deported, not the businesses that hire them illegally. But then Food, Inc is a cornucopia of outrage and it is important that you see it at your local multiplex. Ha.
I read a review of Methland in the New York Times, a book that explores the life of an agricultural town in Iowa that has been devastated by the meth epidemic. Why? Because its citizens are now working for industrial farms, and their labor is so dehumanizing, they'd rather cook up meth in their kitchens and set fire to themselves in a drug induced haze. I wish this connection had been made in the movie.
This is an activist movie, so it's interactive, if you so desire.

The height of marketing chutzpah:
Some house guests of mine bought a two liter bottle of Canada Dry Ginger Ale with Green Tea and Antioxidants. This is an unintended corollary of the good work of people like Michael Pollan, who are trying to teach Americans how to eat healthily and ethically. The corporations steal his nutritional mantras and apply them to their crap. So now you can guzzle Ginger Ale that may cause your teeth to rot and your kids to have diabetes and delude yourself that you are getting nutrition out of it.

By the way, I'm writing a letter to Coke asking (as a consumer, I'm sure they will listen) them to make Coke with sugar cane, as opposed to high fructose corn syrup. It's tastier and it is a little better for you. Mexican Coke is made with sugar and it is less cloying and much better than the local one. As far as I could tell from the labels of Coke in France, they use sugar cane too. I'm sure it is because both Mexico and France are trying to protect their agricultural interests. You can try Mexican Coke it if you live near any Mexican bodega.