Pretty Much every major fight in the series can qualify.
Hishigi is a walking CMOA. He´s a Badass Bookworm who keeps himself alive by implanting Medusa Eyes into the left side of his body, horribly disfiguring him but keeping him alive if he stays out of combat (but still in excruciating and constant pain). He is the strongest of the Taishiro according to Yuan (who is a cocky bastard and does not say that lightly), wields a BFS that makes Kyo´s giant katana look like a little bitch, can cut things at the speed of light so hard that it creates giant shockwaves, one of which is able to put Kyo down for the count (Kyo wasn´t prepared for it, but still) AND he also looks the part of the massive badass. Oh, and did we mention that about twenty years ago, he absolutely crushed Shihodo, who was one of the original Taishiro and who even scares Kyo.
This needs to be emphasized: He ONE-SHOTTED the main character, rendering him unconscious for a whole volume. Granted, he attacked by surprise but still, the lack of effort it took to take even Kyo down is awesome in itself!
His crowning moment however is when he gets the shit beaten out of him by Kyo´s last sealed power (which he gradually recovers the more he is in life-threatening situations), loses all his Medusa Eyes and is apparently too wounded to continue. He then gets up, implants his memories into Akari so she might find a cure to the Death Disease, locks the band of heroes in a force field, does a Taking You with Me with Kyo FOLLOWED by him crawling to Fubuki, while dissolving, and ripping out his own heart and implanting it in Fubuki so that he can keep living before finally disintegrating. DAMN.
Another moment that stands out is Hishigi's fight with Yuan. They are two of the strongest beings in SDK Universe and it's shown quite during their epic clash. Too bad the fight is interrupted.
Can we talk about Hishigi being heavily implied to be the Badass Gay and not being stereotyped in the least? He is possibly the most badass goddamn thing in a manga full of badass goddamn things, and who the fuck cares if he likes men.
Hotaru Vs anyone. Then, you get that part where he out-speeds Yuan in the same fashion Yuan did to him earlier in a fight
Hotaru: You're slow, Yunyun...
Akira's fight with Tokito definitely stands out.
The Look on Fubuki's face when he got smote by Kyo's Seiryuu. EPIC!
Also, Kyo vs. Kyoshiro. End of discussion.
Julian, the father of Yuan, while not being as strong as many other characters, manages to get three of these.
He appears for the first time on top of a literal pile of corpses, playing chamitsen.
We learn during his introduction that he is the greatest blacksmith of the Mibu clan, that Muramasa was his disciple, and that he forged the blades of the Taishiro. Informed Ability, you say? Well, that's until you find out:
That he is able to "wake up" the full potential of any blades (a thing that usually requires a perfect understanding of the blade and its "spirit").
During the fight against the Taishiro, he impales himself on Hishigi's blade to save Yuan. After Fubuki and Hishigi laugh at him for being only a "blacksmith and not a fighter", they realize he's planted needles in the guards of their sabers. Julian then calmly tells them that, since he's the one who forged those blades, he knows exactly how to break them. Cue the blades completely dislocating themselves. They don't stay that way, because Fubuki's necromancy can apparently even resurrect objects, but it's an awesome scene nonetheless.
Bontenmaru, one of the Shiseiten, is a big, tall, arrogant, brash guy with a Badass Longcoat who fights with a bokken. First, the fact that he can hold his own against any katana with a wooden blade is telling something. Then, we learn that every member of the Shiseiten has his own special technique, such as ice mastery, or vampiric powers. Bontenmaru's one ? Dropping his sword and his coat, going berserk and fighting with his bare hands. Now that is awesome.
The first time we see the Shiseiten fight together,against an undead army. Not only are they vastly outnumbered (as in 4 vs. hundreds) but they make this "war" a game in which they compete to see who will get the most kills. By the end of this,the court they were fighting in is completely razed and they are intact.
"4 vs. hundreds" ? Try 4 vs. one thousand undead, regenerating soldiers.