Now the big boys are coming out to play. Which game has some of the best power spells out there to make you smile in sadistic glee?

Lufia's Thunder was very nice.
Chrono Trigger's Mega Bomb made me giggle. "Bomb, bomb, bomb, okay. Oh, and to top it off, here's a nuke."

However, I call shenanigans on Lufia II's "spells". Those are clearly summons, and that is a different class of magic entirely.

I have to go with Lufia's Thunder as well. Sweet dead baby jesus when I first saw that my mouth hit the floor. To this day it just exudes destruction and I love it.

Even though I'm at least 10 MONTHS LATE!!! on this... If it still matters then Lufia II spells hold dominion over all others. Like the monkey said, summoning just steps it up to a whole new level. Specifically the Thunder spell.
Special mention to FF6 though.

I didn't really find Chrono's spells any good at all. To me they just seem bulky and uncoordinated. Though they may have just been going for sheer power!!!

Uncoordinated? How so?

Well.. to me it just seems that they're just throwing their magic around and hoping it hits their target. Whereas if you look at FF6, FF4 and Lufia they attack individually and accurately.

But like I said before, they may have been going for the SHEER POWER!!! aspect.