Fullerenes are a class of materials that may have an impact on the 21st century greater than any other. Fullerenes are molecules composed completely of carbon in sphere or cylinder arrangements. These are called "buckyballs" and "buckytubes".
Buckytubes are about ten times stronger than steel with a weight comparable to graphite. They are extremely conductive, and the strongest fiber known. They would make an ideal armor, or component for prosthetics. Fullerenes, if they could be mass-produced, would be an ideal building material, and could be used to build towers many dozens of miles tall.