Sapiens - This is incredible and a relatively easy read. It charts the path of humanity from the neanderthals to the modern age. A sequel called Homo Deus is equally brilliant; it focuses on the future of humanity.
The Looming Tower - This is one of the only non-fiction books I've reread. It's exceptional. Tells of the origins of Al-Qaeda and all the factors that culminated in 9/11. It's deep but very much worthy of your time.
The Warmth of Other Suns - Currently reading this. It's all about the black migration; the movement of millions of blacks from the southern regions of the US to the more prosperous states; instigated mainly by discrimination and the evils of segregation. Again, it's deep but the writing is superb and weaves together several inspiring narratives.