Freakonomics, by Steven D. Levitt, and Stephen J. Dubner is all about, as the authors but it, 'The hidden side of everything.' Now as generic as such a mantle might sound, Freakonomics really does live up to it's motto in a series of analytical observations on the relationship of various subjects that may seem rather unrelated. Furthermore Freakonomics also disproves certain obvious causes to events or effects in the same manner.
Freakonomics looks at primarily two statements and applies them in an effective way. Enough abstract talk though, lets observe a real example. Take an election campaign, in which one candidate is more appealing than the other to a small base of donators, and raises more money for such a reason and, wins, by a large margin. Because of this, has he won because of the money, or the appeal that allowed him to get the money? At first glance, a subject like voter appeal seems difficult to quantify, but Dubner and Levitt shine through with the explanation of how the candidate is measured up in consecutive elections against the same opponent to prove the point, with large spending shifts only changing voter base by ~1%.
Freakonomics is overflowing with these examples with further data and observations. The only real problem I have against the book is that it feels so short. As you read, you want to know more and more in-depth on the subject and suddenly Freakonomics whisks you away from sumo-wrestlers to real-estate agents. It gets highly detailed and enlightening and then sets course for another subject. And the book itself ends in the same way. It's easy to realize the book is coming to an end when things seem to be haphazardly wrapped up and then disappears leaving you wanting another analysis of a traditionally non-economics subject in a quantitative way. In short, the book feels too short, and rather than a folly of the author's laziness, a quick look back shows how well and enticingly written Freakonomics is.

One would be well advised about opening Freakonomics with an open mind however. The book touches on some sensitive topics such as abortion and crime, and takes a much emphasized stance on them.