Drakensis' Lovehammer stories focus on Angron. It would be tempting to say that all he does is a crowning moment of awesome, but let us settle for Chapter 13: Question of Identity VI.
"This is how I refuse."
The final fight between the Deamon Tazabdulog and Trygg.
Old man Ruith's introduction to the Imperium. Where he manages to piss off Mortarion, his Astartes, Sailor Morta, and several Imperial guard regiments as he runs around as a deliberate distraction. Oh and he steals a commissonar's hat for his own personal use in the process. AND manages to get away unscathed.
The sheer epicness of the fight scene between Huron Blackheart and The Captain in The Scattering of Serenity.