The edges of omnipotence

As christians, we often take refuge in the idea that God is omnipotent. But exactly how omnipotent is omnipotence? Is it possible that there are things God can't do? I think it's not only possible, but crucial to a true understanding of His character.

Think of it like this: If God is both loving (i.e. unselfish, and willing that others should be happy) and omnipotent (i.e. able to do ANYTHING), there should be no pain in the world. The existence of pain implies that either there is some motivation greater than love that is causing Him to permit pain, or that he does not have the power to stop it.

The contemporary christian explanation for this is that God can't take away our pain without taking away our free will, and thus taking away our ability to love and be loved. After explaining that in one breath, the typical evangelical will triumphantly exclaim, "You see, it's his love that keeps him from putting an end to our pain!"

But the question remains: Who, or what, made the universal "law" that a being cannot love or be loved without free will? If it was God, then obviously his character must once again be called into question. If it wasn't God, then He must exist in the context of a set of "laws" he cannot break, even if he wants to. God can't have his cake (a lovable and loving creation) and eat it, too (absence of pain), any more than we can.

Right?