Capital

Norm has a splendid post by Francis Wheen on Marx's Capital:

While all that is solid still melts into air, Capital's vivid portrayal of the forces that govern our lives - and of the instability, alienation and exploitation they produce - will never lose its resonance, or its power to bring the world into focus. As that New Yorker article concluded in 1997: 'His books will be worth reading as long as capitalism endures.' Far from being buried under the debris of all those toppled Stalinist icons and statues, Marx may only now be emerging in his true significance. He could yet become the most influential thinker of the twenty-first century.

Go and read Wheen's piece and then go and read Capital.