Here's a millennial question: What was the most important invention of the past 2,000 years? John Brockman, über-agent for science and technology authors, posed the question to his online community of scientists and scholars and posted the provocative and cantankerous list of responses  on his EDGEWeb site.
Some nominations were obvious: the printing press, the contraceptive pill, the atomic bomb and the computer all received multiple votes. Suggestions ranged from the concrete (the battery, the steam engine, hay) to the abstract (calculus, quantum theory, evolution, double-entry accounting); from the world-historical (religion, the city, democracy) to the quirkily mundane (the eraser, reading glasses, plumbing); and from the physiological (anesthesia, DNA sequencing, aspirin) to the philosophical (the scientific method, "the idea of an idea").
The list makes for an enjoyable read -- if you can get over the participants' utter inability to remain within the question's 2000-year bounds. Suggesting that the most important invention of this era is the spirit of rebellion against arbitrary rules.