Good article on Social Earth describing the emerging fourth sector of socially-oriented businesses. These are firms, both for-profits and non-profits, that are driven by a social mission but employ for-profit business policies and practices.
This is in addition to the traditional sectors - the private sector, government and traditional non-profits. The chart below, from the article, does a nice job of listing the various types of social businesses.
We cover social entrepreneurs and recently posted on alternative legal structures social businesses can use. This is clearly a growing sector and attracting more attention.