It might be a bit presumptuous of me to recommend "essential reads", so I'll go for a lesser "most influential book for me" criteria.

Imagined Communities by Benedict Anderson is pretty much one of the most cited books because it reformulates Hobsbawm's idea of "invented traditions" and Geller's conception of nationalisms into a fascinating mixture. As the title suggests, we "imagine" ourselves into communities through reading literature and "feeling" like we're in a community. There are criticisms to this idea (for example, the postcolonialists would argue "Whose imagined community?"), but it still has a lot of validity to how we envision ourselves as social animals.

The Spirit Catches You and You Fall Down by Anne Fadiman is a masterful anthropological work about the Hmong people in the United States and how they clashed with American medical systems. Both sides are well-intentioned people, but there are cultural and language barriers they aren't able to cross over -- leaving a Hmong child braindead from epilepsy. It makes us wonder "Who is wrong?" at first, but the question is more like "Who is right?" at the very end when we start to understand what it means to "translate" stuff into cultures. If you fashion yourself as a cultural relativist, this book is quite good at challenging your beliefs.

Metaphors We Live By by George Lakoff and Mark Johnson is a really interesting book about how conceptual metaphors define how we actually use language. To put it simply, why do we talk about beautiful people as delicious and ourselves as thirsty? Lust is thus constructed the same way we're hungry for some fried rice. Such metaphors are not just fanciful creative usages but reveals how discourses are set in a certain way.

The Great Transformation by Karl Polanyi challenges our understandings of capitalism being innate in history. As a revisionist history, the work goes over primitive economics and finds that markets don't develop the way Smith and Ricardo have stated. In fact, this happens because Ricardo and later economists argue that economics should not be together with politics. The social is thus disembedded from the economy. So when countries force capitalist developments unto others, they will sever the ties between social relations and the economic modes of production. Polanyi may not have predicted late capitalism, but he is quite close to it. His conclusion is quite powerful too as a statement on how fascism could have developed -- as a resignation toward the failures of liberalism.

Philosophical Investigations by Ludwig Wittgenstein discusses language as a labyrinth and how we confuse ourselves by being a stickler for concepts and definitions. Wittgenstein instead asks us to play language-games with him and look at how there is a sort of family resemblance of concepts in these words. These concepts arise from how we "use" these words. Thus, the objective for philosophers is to clarify how these usages play into these words. His post-Tractatus ideas are still underutilized, but they have done wonders in international law from my understanding.

Mythologies by Roland Barthes is a fascinating overview of what you can do with semiotics onto culture. If the cultures we live in are a text, then can we perform some silly literary criticism and see what these "meanings" are? The first chapter is on wrestling and it goes beyond the "staged performance" crap people talk about and explain why people are into it anyway. If you like Mythologies, I recommend "Empire of Signs" as an interesting Orientalist experiment.

Richard Evans's The Coming of the Third Reich is what it says on the book, but it is also authoritative in its understanding of the rise of the Nazi Germany. Since we live in such troubled times, I figure this would be a good recommendation. I need to go into the other two books as well.

There are some more thinkers who have greatly influenced my thinking as well: Antonio Gramsci, Stuart Hall, Eric Hobsbawm, Zhuangzi, Simon Leys, Simone Weil, Susan Strange, E.H. Carr, Virginia Woolf, and Albert Camus -- to name a few. I am still learning where I stand in the world, so I am always looking for revolutionary writers and thinkers myself. I hope this list helps out you and others.