Cambion
Cambions are the offspring of demons by human mothers. They are also known as Catagos (sp?) or the Antichrist. In 5.06 I Believe The Children Are Our Future, Castiel, corrects the idea that the Antichrist is the son of Satan. The Bible, according to Castiel is wrong, and the Anti-Christ is not the son of Lucifer, but demon spawn born of humans. This lineage makes them incredibly powerful and capable of "killing the Host of Heaven with one word". Because of this Castiel is insistent that Jesse Turner - a cambion - must be killed.
In the 1.01 Pilot, Sam and Dean find a motel room recently occupied by John Winchester, the walls plastered with his research. Amongst all the paper, is one article which talks about Cambion. Whether this is a co-incidence, or a deliberately placed reference remains to be seen.
Links
Wikipedia entry on Cambion
A famous cambion is Caliban from Shakespeare's "The Tempest".
The mage of the King Arthur stories, Merlin, is also often said to be half human and half demon, and was original intended to be the Antichrist.
