The Dan Abnett written ones are all great
If you like all out death and gore, you wanna try out the Gaunts Ghosts books, its just death incarnate.
Titanicus is really good too and hoping there are more in that genre. Horus Heresy is a good series although some of the books are better than others.
Gah, now I've ordered two Dan Abnett Horus books...
Horus Heresy and gaunts ghost it is then.
Just got to figure out which series would be finished first?
HH is one long series, GG is several story arcs.
HH is progressing at a pretty steady rate (2 books a year)