I don't particularly feel like getting into this debate much, since it's one I've been involved in far too many times and no one has ever convinced the opposing side that they are wrong, but the answer to the question "Well, if God created the universe, then where did he come from?" is easy. The answer's already provided in the third possibility posed by the OP.
The laws of this universe (such as gravity, time, momentum, etc.) are all bound to this universe. They exist within this universe and abide by it. Hence, time does not exist outside of this universe. So something that would exist outside of the universe, and potentially be responsible for creating it, wouldn't need to have come from somewhere. It could simply "be there." Time doesn't apply to it.
Regardless, the fact that so many people on here are asking the opposite side to "prove" something (such as prove that God does or doesn't exist, or prove that there's another possibility to God existing, or anything else) is more than a little ridiculous. This debate has raged on for centuries between some of the brightest and best minds the world has known, and no one has come anywhere close to being able to "prove" anything. And no one will unless God shows up and proves it himself. Thinking that anyone on here will suddenly be able to advance past thousands of years of grid locked debate all of a sudden is setting your expectations a bit too high.
