In chapter two, the Ember Trial becomes this with a good enough diplomacy skill. With nothing but some quick thinking and a silver tongue, you utterly demolish Torio's accusations bit by bit, point out every single hole and flaw in her plot, and effectively humiliate her in front of the entire courtroom. And when Torio pulls out her trumpcard, the Sole Survivor of the Ember massacre's testimony, you and Shandra manage to convince the witness that she may have been tricked, rendering her testimony (which Torio's arguements hinge on) moot. And it doesn't stop there. After you're done humiliating Torio in verbal warfare, you and Sand proceed to call your own witnesses, the various people you've helped up to this point, further discrediting the prosecution. Yes, Torio manages to retaliate by forcing a trial by combat, but its clear that she's been utterly trounced. And the kicker? After all is said and done, you actually get a background feat that details how your performance was so incredible, it has instantly become the stuff of legends in the legal community, and your words will be regarded as an inspiration for legal officers for centuries to come.
Related to the above: During your preparations for the trial by combat, Khelgar will burst into the room and insist he fight in your stead. When asked why, he goes on an epic rant about how Torio's actions made the trial a sham, that the coming duel was ultimately pointless and unfair since you had already fairly proven your innocence, and how Luskan's actions have made a mockery of justice. It really shows how far he's come from the arrogant Blood Knight he began as.
And in doing so he unwittingly fulfills one of the requirements to become a Monk: gaining a true understanding of Justice.
Late gate fights, typically in the third act, are something special especially when you know it's a climatic battle and you can cut loose and use everything. The three-way fight between your party, a huge dragon and a encampment of giants is pretty good, and so is the last battle where every possibly party member joins in to kick the King of Shadow's butt.
Mask of the Betrayer
The fight with Araman in the Fugue Plane. LG aasimar paladin 20 of Red Knight / Divine Champion 10, with Safiya, Kaelyn, and Gann at my back. The cutscene finishes, I start to swing the Sword of Gith, then the others hit him with like fifteen spells at once and he's dead in an instant. I wonder how he could have possibly died that fast and look back through the log. Turns out he failed a save on Safiya's Disintegrate.
The meeting with Myrkul. You meet a dead god and walks on his corpse. And after speaking to him and learning that the soul-eater curse, and therefore you, who sustains his very existence, can devour his soul. That's right, ''you can eat the soul of a dead god using a curse that he created to prolong his life.