I hit the Horus Heresy very hard recently, polishing off all of:
Age of Darkness - A short story collection mostly set after the events on Isstvan V
The Outcast Dead - An interesting look into the imperial palace on Terra and the lives of astropaths and other sanctioned psykers
Deliverance Lost - Corvus Corax, primarch of the Raven Guard, and his quest to rebuild his all-but wiped out legion after Isstvan V, also featuring the machinations of Alpha Legion
The Primarchs - A collection of novels centering on Fulgrim, Ferrus Manus, Lion el'Jonson, and Omegon
They were all pretty good, highlights being the material featuring the Lion, Corax, Fulgrim, and Alpha Legion, especially.
I felt I should dig into something more 'literate' after gorging myself on epic Space Marine fantasy, and I'm now reading Moby Dick. It's a classic of American literature, and I'm guessing many read it in school at some point, but I never did. I expected it to be stodgy, archaic, and hard to understand, but I've been pleasantly surprised at how comedic and entertaining it is, and the language perfectly readable, if a little old fashioned. It's fun, so far, though I'm still not too far in.