www.se-alliance.org is the site of the main membership organization that promotes the development of earned income as the principal route to nonprofit sustainability. Its main activity is the National Gathering, usually held in March or April of each year, and this site has a number of very useful resources that members can access.

www.socialent.org, the website of the Institute for Social Entrepreneurs, contains a range of resources and links to resources. Many of these have been produced by the Institute's founder, Jerr Boschee.

www.rolfelarson.com is included here because Rolfe Larson's book, Venture Forth is, we think, one of the most useful guides to the basics of business for a nonprofit. 

www.enterprisingnonprofits.ca offers a very useful tool in the form of the Canadian Social Enterprise Guide.

Try http://www.socialenterprise.org.uk/page.aspx?SP=1892 for a flavor of social enterprise on a different continent.