London Ed offers this quick, over-breakfast but accurate as far as I can tell translation from the Latin (available at Ed's site):
For not every being has a cause of its being, nor does every question about being have a cause. For if it is asked why there is something in the natural world rather than nothing, speaking about the world of created things, it can be replied that there is a First immoveable Mover, and a first unchangeable cause. But if it is asked about the whole universe of beings why there is something there rather than nothing, it is not possible to give a cause, for it's the same to ask this as to ask why there is a God or not, and this does not have a cause. Hence not every question has a cause, nor even every being.
Ed comments, "I'm not sure how Siger's reply falls into the categories given by Bill." Note first that the question that interests me is in the second of Siger's questions, the 'wide-open' question: not the question why there are created things, but the question why there is anything at all. To that wide-open question Siger's response falls under Rejectionism in my typology of possible responses. Siger rejects the question as unanswerable when he says, idiosyncratically to our ears, "it is not possible to give a cause," and "not every question has a cause." That could be read as saying that not every interrogative form of words expresses a genuine question.
Ed also mentions Wittgenstein and suggests that he "had a go" at the Leibniz question. I don't think so. We must distinguish between 'Why is there anything at all?' as an explanation-seeking why-question and the same grammatically interrogative formulation as a mere expression of wonderment equivalent to 'Wittgenstein's "How extraordinary that anything should exist!" Wittgenstein was not raising or trying to answer the former. He was merely expressing wonder at the sheer existence of things.
I would be very surprised if someone can find in the history or philosophy, or out of his own head, a response to the wide-open explanation-seeking Leibniz question that cannot be booked under one of my rubrics. (Credit where credit is due: my catalog post is highly derivative from the work of N. Rescher.)