Three Sisters are Corn, Beans and Squash and they grow great together.
Corn takes nitrogen and beans actually produce nitrogen. Moreover, a tall corn plant is the perfect trellis for pole beans. But who wants to have their corn growing on dry exposed dirt? So plant squash or pumpkins under the corn and you've got a nice living mulch that protects the ground from drying out and shades the land so weeds can't grow.
