The Black has released a new anthology, Blades of the Traitor.
From The Black Library:
The Story
Across the war-torn galaxy, those sworn to Horus’s cause shake the Imperium to its very foundations. Before the traitors’ relentless onslaught, the wisdom of ages past is lost and forgotten, daemons hide amongst the common people and the warp’s corrupting influence can be seen in almost every facet of the Heresy. For those who would become champions of the new order, there can surely be no redemption – only an eternity of carnage and slaughter, and the laughter of thirsting gods...
Read it because
Blades of the Traitor brings you five epic, action-packed tales that drive the Horus Heresy forward. Discover what the Warmaster’s allies are up to as they prepare to march on Terra: sacrifices in the bowels of Molech’s Enlightenment, Legion Navigators delving through the very Eye of Terror and horrific experiments in dark, secret labs.
You can buy the book here.
You can buy the eBook collection here.

In this collection:
Daemonology by Chris Wraight
Black Oculus by John French
Chirurgeon by Nick Kyme
Twisted by Guy Haley
Wolf Mother by Graham McNeill
I already got the book at the Horus Heresy Weekender and bought the eBooks as that is the way I read everything now.
Loken