I recently finished The Omnivore's Dilemma. I can't say enough good stuff about this book. I loved it.
I won't go over all the details of the book (I mentioned it in an earlier post here), but it does a great job of showing how our eating choices can affect the world we live in.
The big insights for me were: how incredibly over-dependent the typical American's diet is on corn (and thus oil), and new insight into how a "beyond-organic" farm could operate.
It really reinforced and confirmed the dietary choices Mary and I have made. Almost all of our grocery purchases come from the co-op, which focuses on organic and local. Our produce is almost entirely local and organic. Our beef is mostly grass-fed (which, it turns out, is actually healthier to eat (not to mention better for the cows/environment/etc.) due to a better balance of omega-6 and omega-3 fatty acids).
Anyway, I highly recommend the book as it not only explains the state of things, how things have gotten the way they are, but also gives you enough information to make changes if you so desire.