I actually haven't read many 40k novels outside of the Horus Heresy but [i]The Siege of Castellax[/i] was a lot of fun. Iron Warriors trying to out-strategy orks, only to find that Orks don't need stupid strategy and can [color=00a651][i]WAAAGH[/i][/color] their way through most plans.

And of course, Deff Skwadron always deserves a mention for its unrivalled, glorious Orkishness.