http://anniegreenjeans.com/tag/interplant/
Also, "polyculture (see wikipedia) mentions that a study in china growing several varieties of rice together increased yield and decreased need for insecticide. Maybe next year I'll grow some other potatoes with the King Harry". This year I'll try several varieties of brocolli, if I can find some other strains.
Also see Gaia's Garden, with a quick review by Chelsea Green,
Also, a quick no-till garden .
Here are some recommended books that I've found useful and informative. Check your local library, or buy from your favorite bookstore (buying from Amazon via these links helps keep GardenHacker.com going).