The stock market crash of October 1929 signaled the end of the "Roaring Twenties" and the beginning of the Great Depression. This was the second day of the big drop, known as "Black Tuesday," which began one day earlier and occupies the next spot on this list. 3.) Oct. 28, 1929 (-38.33, -12.82%)

The uncertainty of a potential trade war led to sharp declines late last week and an extremely volatile trading day on Monday. As a result, Google searches spiked around the stock market crash of 1987, also known as Black Monday. That event refers to the sharp decline the markets saw on Oct. 19.