73. Craigslist

In the summer of 2000, Craig Newmark's San Fransisco classifieds site expanded to seven major cities, and chances are your local economy was never quite the same. Looking for a girl to live in your apartment, tonight? You know the drill.

YOU AUGHTA KNOW:
Craigslist serves over 20 billion page views per month, making it the 8th most popular website in the United States.