These are the ones I have been thinking about most, recently:

Guns, Germs, and Steel

Complexity

1177 B.C.

Sunset Kingdom

Pagans

Guns, germs, and steel deals with the way that humanity's history has been shaped by the flow of resources and information, which I feel is often neglected by people thinking about the future.

Complexity deals with the way that atomized individuals making personal choices end up creating emergent behaviors. With 8 billion people on the planet, understanding those emergent behaviors is going to be crucial to understanding the future. (There are almost certainly more thorough and up-to-date books on this by now. This is just the one I read in high school so it has the most influence on me personally.)

Sunset Kingdom traces modern conspiracism surrounding sinister "Jewish Bankers" and the global apocalypse to pre-Christian, even pre-Roman notions about civilization as the one force that stands between chaos and order in the world.

1177 B.C. deals with the collapse of the Bronze age empires, a situation that I believe is very similar to the modern world in many ways. What's important here is that many of the narratives that we use to talk about the world – empires vs. barbarians – are rooted in this time period and have been passed down with relatively little change.

Lastly The Pagans portrays one of the rarest events in human history: what appears to be a true and dramatic transformation in human thinking, over the course of only a few hundred years.

In my opinion each of these books illuminates forces that shape the future, which futurists often neglect. People who hang out on this forum tend to be excited by new technologies. I know I am. But that means that there is also a technocratic strain that believes that some kind of inflection point, singularity, or other spontaneous transformation is near at hand that will make all of our dreams of the future come true, because the rest of humanity will either recognize the promise of technocracy or get dragged along kicking and screaming.

I sort of agree that there is an inflection point coming, which is why recently I have been studying the only two true such inflection points in history, that I can see.

The first is when humans stopped traveling, became sedentary, and most importantly those sedentary humans began seeing themselves as the "normal" ones, bifurcating human survival strategies in a way that pitched expansionist agricultural societies into inevitable conflict with anybody occupying any land that they wished to convert into their resources.

The second is when massive numbers of people in the centuries around 1 AD, and continuing to this day, began abandoning the notion that time, life, and history are inescapably cyclical, and began embracing the notion that proper belief and behavior could free a person (or an empire) from the cycle.

In both cases, the ideas pre-existed the transformation for centuries, possibly forever. Why did human outlooks shift so dramatically in what appears to be very short periods of time? What idea, currently held by some loony cult, is going to be treated as so obvious in 200 years, as the idea that humans want to live year-round in the same place (except for rich people of course), want to spend their days working instead of foraging, or that we can escape the fate that our eyes tell us is inevitable?

If something like that is in our future, we need to understand how it happened the last time. How did millions of people shift their outlook? How long did it take? What were the transitions like? If population density causes aristocratic imperialism to emerge from human tribal behavior, is it possible that there is some other population threshold where new, more complex behaviors might begin to emerge? And if we don't make it to that threshold, what are the chances that our current state of imperial expansion can continue, for even another half century?