Never have I seen a final boss fried so quickly as with...
Fallen Wings
Sky Dragon Slash
and White Apocalypse.
Bastard never saw it coming.
Let's also not forget, despite it's slightly Voltron-ish-ness, Erde Kaiser from Xenosaga part 1. Nothing quite says 'badass' like an attack that kills 99% of your foes in one hit.
Also. Flonnezilla. Anyone who has seen this attack in Disgaea 2 knows that it is teh awesome. Even if my level 100 characters can do more damage than it with Flonne at level 500 >.>
Also, Sora's Final Form attack patterns. Killing everything in seconds with normal attacks has to be awesome. Strangely enough, I thought his anti-form was pretty awesome too, even if the floating Organization bosses made it annoying, since you can't jump worth a damn. :rofl: call it Neko-ken Sora. That's what it looks like. And it is crazy-fast.
Okami - Cherry Bomb. It blows shit up. 'Nuff said.
Let's also not forget Ganondorf's Warlock Punch. Doesn't hit often, but when it does, man is it satisfying! One of the reasons no one will play team-matches with me unless they're on my side. I'm not very good, but pitch me someone at the right range, and they're gone.
Also, Hiro's Triple Slash. In a game where most enemy HPs don't break 1000, it kills everything short of bosses. And those it deals massive amounts of hurt to. Zophar took time, one of the few final bosses with enough power to believably be a god of destruction. Though he was, of course, not even a challenge for me. Put the Fiend Ring(insane defense, strong vs. EVERYTHING, but you start every battle with less than 20 HP) on Ronfar for that battle and as long as you fry the two hands you can before part 2, he doesn't stand a chance and all you've got to do is wail away.
And on the subject of VP... Lenneth's Nibelung Valesti is also awesome. Even if it doesn't deal 10000 damage like Freya's Ether Strike at the very beginning.
Also, nothing yet has defeated the overpoweredness of Ultima from FFVI. Give Terra the Economizer and Gem Box, and everything just kind of fries. Even the final boss doesn't last long against that, and all the rest of the party has to do is sit back and keep healed.
And I should probably stop now...