Sons of Guilliman
The Sons of Guilliman are a successor chapter of the Blood Ravens f(actually, according to 6th edition, they are now Ultrasmurfs. Goddamn Ward stool corrupts GeeDubs) sounded sometime in the 33rd Millennium. Not much is known about them besides they are 'proud and noble' (like any successor of the ultrasmurfs then).
There is fluff regarding two battles that the Sons have taken part in; the Third War of Armageddon where they sent six companies to help battle the Orks, and the Cleansing of Salinas where the Sons fought a force of chaos warriors who could bend reality and eat men whole. This battle ends in tragedy for the Sons where their force at the cleansing gets wiped out, only for a force of silver warriors to smite the foes with lightning and faith (Grey Knights to the rescue again hey?). Although it ended badly for the Sons at least they are mentioned in a source. Thank you Graham McNeil for doing your bit again to expand the fluff.
The Sons have a sweet but difficult colour scheme which means only the best painters will have a chance of doing it well. It is blue and white quartered diagonally so you have to have steady hand or a machine doing it for you.