PC World dedicated an article to the history of pi to celebrate Pi Day (because today is 3/14), you can check it out over here.

Everybody knows that the value of pi is 3.14…er, something, but how many people know where the ratio came from? Actually, the ratio came from nature--it's the ratio between the circumference of a circle and its diameter, and it was always there, just waiting to be discovered. But who discovered it? In honor of pi day, here's a brief (sort of) history of how pi came to be known as 3.14(1592653589793238462643383279502884197169…etc).