After The Horus Heresy and The Siege of Terra... what next?

[Todd]

Besides the soon-to-released Era of Ruin, what other books are out that bridge the gap of "After Horus" and "Before the 41st Century"?

Any book series that cover The Scouring?

[Avery]

Word on the rumor mill is that Black Library is thinking about starting a Scouring series, but for now there is nothing set in the immediate aftermath of the Siege. Most references to this period are just lines from assorted books (mostly about traitor marines).

Some of the older series (Astra Militarum, Gaunt's Ghosts, Ravenor/Eisenhorn, etc) are set generally in 40M, before the major story arc with the 13th Black Crusade and the return of Guilliman.