Legend of Legaia on the PS1 and its sequel Legaia 2: Duel Saga on PS2.
Two really great games, IMO. They're Final Fantasy style turn based RPGs with a twist- the combat style, while turn based, drew heavy inspiration from virtua fighter style fighting games. Each round for each character you would input a series of attacks to fill up something of an "attack meter", which grows longer with more experience, and then once you're done the characters would unleash the combination you just input. By putting in these combinations you could unlock certain special moves called Arts, which look more impressive and do more damage. You could even link arts together in combos to do some major damage.
Especially in Legaia 2. Between being a a very high level, using multiple powerups to boost my strength, and linking up some of the most powerful arts attacks in the game, I once did a combo that took off well over a million HP. Killed off the final boss in one glorious shot.