Last night I went to see Food, Inc. with a few friends. In many ways it was a horrific, but very educational movie. I would encourage everyone to go check it out because I believe it covers information that everyone needs to know. The basic gist, though (for anyone who doesn't have the time or money to sit down at a movie for two hours) is that all of our 'industrial food' is owned and run by a handful of very wealthy, very powerful companies. They are taking the nature out of natural things (like the animals that we eat), and engineering mass produced alternatives that save time and money. You will never see a better testament as to why we should all eat local and support farmers who are still doing things the old fashioned way.
The issue of food is pressing, and surpasses politics on many levels (as animals we need to eat, and we should probably be eating good things.) There are lots of books out there on the subject. I have heard that The Omnivore's Dilemma is a good one, and I can personally recommend Animal, Vegetable, Miracle. Half this battle is getting educated and educating others. Reading a book is a good way to do that.
For me, the most important (and applicable) quote from the movie was something along the lines of "every time you ring an item through the checkout, you are voting with your dollar." This is true of food, but it is also true of every other thing you buy, ever. Rick Ridgeway from Patagonia talked a lot about voting with your dollar when I saw him speak at UCLA. The world is run by money (whether we like it or not), and people are watching every time you use your money- anywhere. It is our responsibility to be conscious consumers as well as conscious designers.