Dragon's Teeth Corsairs
Founded near the end of M36 by Ladon, a powerful solarite. He lead his growing army of followers away from Commoragh to escape the Glass Plauge. They escaped and thrived, preying on ill defended planets and trading vessels. After the plauge was annihallated, few of his followers returned to Commoragh. Some stayed out of fear of Ladon's wrath; others, out of loyalty. However, the majority of the Xenos stayed so as to be part of the constant raids that accompanied being part of the corsairs.
The Spectral Cult
The Spectral Cult first began their attacks against the Imperium in the beginning of M38 after fleeing from Commoragh for reasons unknown. They have been seen fighting alongside the Dragon's Teeth Corsairs, though their alliance seems tenuous at best. They are masters of webway travel, and have on several occasions traded knowledge of hidden portals to the corsairs in exchange for unusual and rare weapons, or, more often, the rights to lead a realspace raid. On one such occasion, Ladon refused, resulting in a civil war that decimated both parties.
Coven of the Shards
The Coven of the Shards helped the Dragon's Teeth Corsairs escape from commoragh during the plague of glass. The price, however, was extremely high; A soul trap was implanted in the eye socket of each of Ladon's original followers, ensuring their loyalty. Since they formed their pact, the corsairs have served the coven, and the coven has watched over the corsairs, regenerating the fallen and providing re-enforcements when necessary.