I thunk an interesting philosophical question on this subject the other day:
Suppose I'm riding in a car, with three friends. One person in another car intentionally crashes us. All five of us are killed.
There are several things that people might say about this incident with respect to free will:
No free will
God, or destiny, caused the accident. Why? Because it was destined. What about the driver of the car who intentionally smashed into my car? That was not intentional, it was God's will, or destiny if you like.
There is then another consideration to be made: this makes murder morally acceptable, because there are no evil actions, as we can't help what we do, since it's all part of the plan. This is a scary point of view, held by some Christian fundamentalists: they let their children play in the middle of the street, because if God decides to take them, who are they to complain.
Obviously this logic is severely flawed, but what of God then? There are evil actions, God is by definition not evil, ergo there must be free will. Which brings us to:
Yes free will
The driver of the car caused the accident; it was intentional. Why? That driver made a choice to do so. But if it wasn't destined that we died, then why did God allow it? One answer is that God doesn't exist. In that case the discussion is over, as all our actions are decided by ourselves (getting in the car that would later crash) or other people (causing the accident).
In my personal philosophical musings, however, I am assuming that God does exist. I also firmly believe in free will. And I don't think the two are incompatible. I read in another node (can't remember which) on this subject an interesting proposition:
God does not create the future, he only knows it.
I tend to agree with this. I suspect God could mess around with things if he wanted, but generally doesn't. This is how free will and omnipotence/omniscience can be compatible.