Founded: 1995
First Address: 1010 Cole St., San Francisco, CA
Newmark's classified-ad site grew from humble origins: a list of notable upcoming events that he e-mailed sporadically to Bay Area friends. He worked out of this two-bedroom apartment on Cole Street for six years; he moved the company to nearby offices in 2000 but lived here until he sold the apartment in December 2005. Now 17 million people visit Craigslist each month.