Simon's most important contribution was to crystallize and explain an insight that even the best economists before him only glimpsed -- namely, that human beings in free societies are "the ultimate resource." Nothing -- not oil, not land, not gold, not microchips, nothing -- is as valuable to the material well-being of people as is human creativity and effort.
Indeed, there are no resources without human creativity to figure out how to use them and human effort actually to do so. Recognizing the truth of this insight renders silly the familiar term "natural resources."
UPDATE: Mark Perry looks back at Simon's famous winning bet with scientist Paul Ehrlich (author of The Population Bomb).
No resources are "natural."