Just recently I heard about this ancient method of companion planting, so-called "the three sisters" by the Native Americans. As depicted in the illustration above, the 'three sisters' are corn, beans and squash; in this planting style, each corn plant is paired with a climbing bean, while squash are planted in between. Corn stalks provide a trellis for the beans to wind around, while the squash becomes a ground cover. Corn needs a lot of nitrogen to grow, and since beans are a heavily nitrogen-fixing plant, the two are ideal companions (though this year's bean will contribute nitrogen for next year's corn). The squash acts as a mulch, preventing the growth of weeds.
The 'three sisters' planting method has been passed down through many Native American tribes, and it's fascinating that they developed this agricultural practice without an understanding of the science behind it. They believed there was a spiritual match between the three vegetables -- corn, beans, squash -- and this belief was both engendered and supported by the success of the plants as they grew together.
Here is a link to a more detailed description of how to create your own three sisters garden. There are also many books and websites to look into if you are interested in companion planting, which I believe is an important part of every garden and something everyone should be aware of as we move toward a future of smaller-scale, sustainable agriculture (I hope).