What would convince me of the existence of God?

In response to Manic Street Preacher's blog-post on the recent Premier Christian Radio Unbelievable? discussion between Lewis Wolpert and Russell Cowburn, I made the following comment (quoting MSP first):

I have often been asked what evidence that I as an atheist would accept for the existence of God.

I can’t say that I’ve often been asked this question, but I have heard it put to atheists enough times to make me consider what my own response would be.

And I don’t know. I think an ostensibly supernatural experience would most likely make me wonder about my sanity before I would accept that the cause of the event was divine intervention (although Lewis Wolpert’s example* would, I admit, be pretty convincing).

My answer to the direct question would probably be a request for clarification of the term “God”. I might be convinced of the deistic wind-up-the-clockwork-of-the-universe-and-throw-away-the-key type of god, but the God of Abraham seems so utterly ridiculous and untenable in so many ways, I simply have no idea what could possibly convince me of his existence, other than the most obvious, miraculous, personal revelation, in the presence of others whose sanity and corroboration I had no reason to doubt.

But really, there’s no need for me to be concerned about this. If the omni-whatever God of Abraham really exists and really wants me to believe in him, he knows perfectly well what it would take to convince me, even if I myself have no idea — and yet, so far, he appears indifferent to my lack of faith. This leads me to only one conclusion.

On a related note, I see that MSP has provoked the ire of William Dembski's Uncommon Descent bloggers (who incidentally seem to have got hold of the wrong end of the stick — so what's new?).
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*Wolpert suggested that having his deceased wife returned to him would probably be enough.