Hemant Mehta, the Friendly Atheist, had a conversation with a pastor at a megachurch. It's a nice little talk, about half an hour. Worth your time.
At the end the pastor asks what it would take to get Hemant to believe and Hemant basically replies that it would be nothing less than a personal revelation. Others' miracles or revelations, nor scripture just don't cut it. The pastor then tells the audience, paraphrased, "Hemant's not asking you to pray for him, but if that's what you want to do, then that's what you should pray for." I don't really understand why their god needs for them to pray before he understands that that's what Hemant would need, after all Hemant just said that, and I thought we were talking about a superior being of some kind? Whatever; that's not actually what I want to talk about.
I disagree with Hemant. I don't think that personal revelation would cut it. Even if I had the sort of joyous, numinous, soul-shatteringly awesome revelation of personal contact with the almighty... that wouldn't be good enough. Simply put, consistency demands that I not accept that as evidence of the divine. It's not good enough for me if someone else has that experience, and I can't claim that they have not, so it can't be good enough for me that I have that experience. Even though I would have experienced something amazing, it wouldn't count as evidence. Because it's not evident; it's not verifiable, it can't be checked, it can't be examined in any way. That's what "evidence" means, "that which is seen". It means "out in the open". That's why personal revelations, whatever they are and whoever receives and whoever they may be from, simply don't count as evidence. Since I don't accept such from other people as evidence for their deities, I couldn't accept it even if it was my own experience, rather than someone else's. It's important to me that I be consistent in my beliefs and behaviors; my desire for personal integrity means that if I were to be visited by the holy spirit and fall to me knees in awe... I would have to get up and walk away saying, "That was incredible, but it's not good enough."
And I think that may be why atheism can be such a bitter pill for the faithful to swallow. Part of the reason, anyway. It's because they relate one of the most amazing, wonderful, defining experiences of their life, and my response is to shrug and say "That means nothing. It may be very meaningful to you, but it's worthless to me." I don't, and wouldn't, say exactly that, but that's what my position boils down to. One of the central dogmas of any religion, even a semiatheist one like Buddhism, is that that wonderful experience is the ... hell, it's not merely the central dogma, I think it may be the defining fact. The ecstasy of worship why people come back, it's why they believe. The rest of it is just the floating rationalizations, the political dander, the shell of ritual. That ecstasy is what makes religion convincing. They're directly experiencing the divine.
Or so they believe. Some research may indicate that it's all in your head, a heightened emotional response triggered by religious stimulation. To put it another way, a braingasm. Even if that's completely off base, though, even if that research is shown to be a complete misinterpretation, there's still no evidence to indicate that the ecstasy of worship is in any way related to an extant being. It's simply not evidence of anything beyond the fact that some people experience that response to worship. And it wouldn't be evidence even if it happened to me.
So what would it take for me? I don't know for sure. What I do know is that, AntiCitizenX put it on Youtube, if an object exists, then there is some action A that would yield some result B where A wouldn't result in B if that object did not exist. So to convince me your god exists you would have to first define action A, show how your god's existence would result in B (whatever B is), and prove that B wouldn't result from some other cause. If B could result from another cause, you'd have to show first how often, so that could be taken into account, like taring a scale. In short, if your god exists, you'll have the burden of proof to demonstrate that some event is best explained only by your god. Otherwise...