The return of Captain Severus in a massive Roaring Rampage of Revenge right through the ranks of the Black Legion. Subverted when it turns out that it's actually the Daemon from before wearing Severus' body as part of a complex Batman Gambit.
Karnak the Chaplain gets one with two simple words.
The Chapter's Due is a whole Crowning Moment of Awesome for the Ultramarines. Having suffered several years of being a Creator's Pet in terms of fluff, Graham McNeill proves just why the Ultramarines are held as the standard for Space Marines: they're actual human beings who treat their people with dignity and respect.
Marneus Calgar: Having previously lied to his own Chapter about killing M'kar, Calgar uses the Shard of Erebus recovered by Uriel Ventris to kill M'kar. He emerges as a humbler man from the battle.
Varro Tigurius: At his absolute limits, Tigurius manages to wake up long enough to sever M'kar's link to the Warp core aboard the Indomitable, making him unable to raise anymore daemons.
How he did it is a crowning moment of awesome as well: being carried along by the civilians of Talassar who had gathered in the citadel of Castra Tanagra. The leader of civilians is holding Tigurius' staff, which is larger than him. Even Calgar finds it a CMOA.
Uriel Ventris gets a crowning moment of awesome with this line: "I name thee Maloq Kartho! Your true and mortal name!"
Where Uriel defeats M'kar by invoking its True Name and thus allowing Marneus Calgar to stab it with the 'Shard of Erebus'. Made more awesome by the fact that Word of God states plot points in the book hearken to the darkest and most secret times of the Horus Heresy - the Shard of Erebus seems to be a part of the Anathame.
Pasanius gets one when he takes a melta blast to the chest. His armor is reduced to dripping ceramite, yet he survives unscathed.