For years I've heard this question from children in the first and second grade and I have always been tickled by the discomfort it creates with Sunday School teachers. "If God can do anything, can God create a rock so big that God couldn't move it?" This is one of those tricky questions that you can't answer without nullifying the qualifying statement that God can do anything.
There's a word for the notion that God can do anything: Omnipotent. It means literally all powerful. A quick scan through a Bible concordance, however, reveals the word is never used in scripture, though the concept of being all-powerful certainly seems indicated. God created the heavens and the earth. God created life. God brings the dead to life. God can take away life. God can change the weather and even push the sun backwards across the sky. The Bible is replete with examples of the powers of God.
But can God do everything; is there nothing God cannot do?
Here again, one's theology of the scriptures, and even one's theology of God, is put to the test. The Bible clearly says, "For God, all things are possible," leaving little doubt to many that God is indeed all-powerful. But the human factor in the equation seems to gum up the results.
In the second creation account and the story of Adam and Eve God creates a couple with a will and a mind of their own. For whatever reason, God creates humanity with a mind of its own and then leaves it to its own devices. Adam and Eve bite the forbidden fruit, very much against the will of God. The next several generations get things so badly that God decides to destroy them all and start again, sparing only Noah and his immediate family. The whole Bible is filled with person after person, nation after nation rejecting the will of God for the sake of their own desires--and God seems unable to change them.
Of course, one solution to the dilemma is to submit, "It's not that God can't, but that God won't intervene."
However, in one instance it is clear there are some things God can't do. When Christ visited his hometown he "could do no deed of power there, except that he laid his hands on a few sick" (Mark 6.5). Hence, we are clearly told there are things Christ/God could not do. In the same manner, God does not seem able to make us happy or make us obedient, among other things. In any event, if God is somehow limited in one instance of power, perhaps there are others as well.
So it seems the question we're asking (back to the big rock question) may be based upon a false assumption. Perhaps God can't do everything, and if not, perhaps humanity might become a bit more responsible about how we treat the creation God made and how we deal with each other (oops, wrong soapbox).
So can God create a rock so big God can't move it? No and no--maybe.