Beans, corn, squash
One of the more commonly know plant associations is beans, corn and squash. It is a First Nations planting method that goes back for several centuries and is often associated with the Iroquois.
Now corn is not often a crop that a backyard gardener, unless the backyard is a good size will plant but it can be a great community garden crop and the sisters can make an excellent shared garden within a community garden.
However, if you have the space or simply want to experiment then the 3 sisters will increase your yield and reduce your labour.
The three plants work together to help one another grow and help the grower get a healthy crop. The beans grow up the corm stalks and provide the nitrogen that helps the corn grow and the squash is planted between the corn rows and acts as living mulch and thereby reduces the need to weed and water.