I did a pretty cool party once:
Knight, Thief, Scholar, Geomancer

The Knight and the Thief would attack, the Scholar would also do so, with his elemental books he could deal the same damage as a Knight (If the enemy had any element though.) The Geomancer would cast his powerfull and free magic, and if I felt like, I could bring him to the front to attack (He had a very high atk power, but had low defense.)

There was no necesity for a healer, the Thief stole High Potions from the enemies, and the Scholar would use them to heal everyone, + the Knight's White Magic, I didn't need any more healing. Since the Scholars doubled the effect of the items they used, and had high Inteligence, those Magic-Casting items were really usefull, I once did like 2000-4000 damage against someone, but I don't remember.

So: Everyone has High Atk, even the mages, which can also cast powerfull magic, and they don't need a White Mage since they have enough healing capabilities.

The Problem of that party is that it only works for a short time. From the Fire Crystal to the Water Crystal, that's it. After that it turns very weak, but I liked it a lot.