Earth surrounded by antimatter belt
A thin layer of anti-protons around the earth have been spotted by the Pamela craft. Anti-protons, as the name implies, are the anti-particle of protons, with a charge of -1 instead of +1, but their other properties are the same. However, if a particle and it’s anti-particle come into contact, they will annihilate each other.
An interesting application of this is as a potential fuel for spacecraft, which NASA has some interest in. If I remember correctly, anti-matter powers the Enterprise in one of the Star Trek shows, which just goes to show that good science fiction has a basis in science.
UPDATE: a grand total of 28 anti-protons have been found, which is probably not enough for any practical purposes.