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10 Brilliant Marketing Ideas

From radio to YouTube clips, 10 companies that changed everything.

This story appears in the February 2010 issue of Entrepreneur. Subscribe »

1. 'A diamond is forever'

Backstory: Diamond prices were sinking fast in 1938, so De Beers mining company enlisted ad agency N.W. Ayer & Son to help reverse the trend. A year later, it launched the "diamond is forever" campaign and brazenly promoted the idea that every marriage required the gift of bling. And plenty of it: It also invented the "two months' salary" spending rule.

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