http://seomoz.org/ by Rand Fiskin is a college dropout who started blogging about SEO (Search Engine Optimization) back in 2004 while working for a family-run web development company. He was also providing SEO consulting services to a few small clients.
SEOmoz has since left the consulting business and instead focuses exclusively on creating awesome SEO software, as well as supporting a large community with educational resources related to the search industry.
It is rumored that the company generates millions of dollars each and every month from its software and subscription services. The company also raised $18 million in 2012, which it has been using to acquire other companies. Rand is still actively running the company and occasionally posts on the main blog.