(or the green Savior)
Cannabis.
-Produce 4 times more cellulose (to make paper) than wood on the same surface every season (a tree takes years to be usable).
-Its fiber is better than cotton AND ecological. Used to make anything that use fibers (clothes, accessories, rope, etc).
-Cultivation-wise it has the qualities of a "bad" weed : hardy, prolific, low maintenance (ecological and economic).
-Produce a healthy cooking oil. The oil can also be used for fuel.
-Quality, tasty food, drinks and protein can be made from it.
-Marijuana has a wide range of medical uses (painkiller, anti-glaucoma, appetite stimulant for cancer and AIDS patients, etc). With no nasty side effect.
-Cool looking leaf. Decorative and symbolic.
-Last but not least. The safest recreational drug. Would prolly be voted The best recreational drug in a worldwide poll.

Personally I use it only to get high (you prolly do too) but the other uses make a lot of people and the environment happy too.