Interplanetary Classified
Did I ever mention how much I love Craigslist?
I can't think of any other company/service which has maintained such a consistent committment to its core philosophy over the years.
Part of this is simply not-going-public, but the vast majority, I believe, can be traced back to Craig himself.
Other companies buy up superbowl ad-time for promotions. Craigslist sends their ads into outer-space.