Kryptonite

Kryptonite is a radioactive chunk of the planet Krypton. There are a wide variety of types of Kryptonite. Among them are:

Green Kryptonite
Green Kryptonite, although rare, is the most common type. It is harmful to natives of the planet Krypton. It can drain their strength, and eventually kill them. Green K is often used by villains as a weapon to destroy Superman. In fact, Green K was a key element in Doctor Natas's Noxium crystal.

Red Kryptonite
Although Red K has no fatal effects on Kryptonians, it's effects are still unpredictable. It could give Superman extra arms, or it could even turn him into a child. It could do a ton of other things. Red K is unpredictable, there's no telling what may happen.

Blue Kryptonite
Blue K isn't harmful to Kryptonians at all, in fact, when injured, it can heal them. However, it's effects on Bizarros (such as Bizarro himself) is deadly.

Gold Kryptonite
Gold K is capable of removing a Kryptonian's super powers permanently. There was only one known chunk in existence, and it was destroyed by Firestorm.