United Dairy Farmers based around Cincinnati is one co-op you might find interesting. They are an ice cream shop / convenience store / occasional gas station (I know it sounds strange) that has grown to ~200 stores in our tristate area. I wish there more info about them online.

http://www.udfinc.com/about-udf

The founder and family made Forbes' billionaire list.

http://www.forbes.com/lists/2006/10/S22J.html