Take MN 63, for example. In this exchange, Malunkaputta demands that the Buddha answer ten questions concerning positions that are "undeclared, set aside, discarded by the Blessed One" — whether the cosmos is eternal or not eternal; whether the cosmos is finite or infinite; whether the soul and the body are the same or the soul is one thing and the body another; whether after death a Tathagata exists or does not exist, both exists and does not exist or neither exists nor does not exist — or else he will leave the Sangha.
The Buddha responds to this onslaught of questions by asking Malunkyaputta, "Did I ever say to you, 'Come, Malunkyaputta, live the holy life under me, and I will declare to you that 'The cosmos is eternal,' or 'The cosmos is not eternal,' or 'The cosmos is finite,' or 'The cosmos is infinite,' or 'The soul & the body are the same,' or 'The soul is one thing and the body another,' or 'After death a Tathagata exists,' or 'After death a Tathagata does not exist,' or 'After death a Tathagata both exists & does not exist,' or 'After death a Tathagata neither exists nor does not exist?'" Malunkaputta, of course, answers no. The Buddha further admonishes:
Malunkyaputta, if anyone were to say, 'I won't live the holy life under the Blessed One as long as he does not declare to me that "The cosmos is eternal,"... or that "After death a Tathagata neither exists nor does not exist,"' the man would die and those things would still remain undeclared by the Tathagata.
As for DN 27, the Buddha tells a story about the beginning of life on this world to two brahmins which, in the end, was used to illustrate how the way to liberation is beyond caste and lineage. So, in this regard, the Buddha does give what can be interpreted as a rough theory of evolution to the pair of brahmins in that the physical characteristics of the mythological beings in question change due to environmental changes and interactions, as well as a description the universe somewhat akin to the oscillating universe theory.
I think that, when taken literally, the creation myth in DN 27 can be seen as an attempt to give a naturalistic explanation of the origins of life and the universe, and Darwin's fairly well-proven theory of evolution certainly isn't inconsistent with this, which makes many new Buddhists breath a sigh of relief. That being said, I agree with Prof. Gombrich that, taking the context of DN 27 into account, this sutta is a lively and ingenious parody that's actually meant to make fun of the very need for a cosmology as a foundation for religious development (How Buddhism Began: The Conditioned Genesis of the Early Teachings, pg. 81-82).
Personally, I see Buddhism as dealing exclusively with mental stress and its cessation (i.e., psychology), not biology, or physics, etc. And while some people get excited when they discover that Buddhism contains teachings which seem to be in accord with modern science, I think they can often be misleading and shouldn't be taken too seriously, or at least, too literally. I think this is especially true of DN 27 considering that recent observations of cosmic background radiation indicate the universe is actually expanding at an accelerated rate, hence there may not be any contraction or 'Big Crunch.' (Lawrence Krauss mentions this in his talk at the 2009 AAI Conference; although it should also be noted that Roger Penrose recently challenged the commonly-held 'inflationary theory' of cosmology with his suggestion that analysis of cosmic microwave background shows echoes of previous Big Bang-like events.)
As for the question of God, that's also a non-issue in Buddhism. According to the texts, a beginning point to samsara (literally 'wandering on') isn't evident (SN 15.3). This can be interpreted two ways — that a beginning point to the continual cycle of death and rebirth of beings isn't evident, or that a beginning point to the continual cycle of death and rebirth of the conceit 'I am,' the self-identification that designates a being (satta), isn't evident — and they're not mutually exclusive. Either way, the point is the same: all that really matters in the here and now is whether suffering is present, and if so, how it can be overcome.
All in all, I think it's safe to say that Buddhism is essentially non-theistic in view. However, I also happen to be of the opinion that, if we dig a bit deeper, the idea of a creator God is incompatible with certain aspects and teachings that, if taken to their logical conclusion, seem to reject the idea of, or a need for, a creator God. For one thing, the logic of dependent co-arising negates the idea of a creator God in that it precludes a first cause or a causeless cause. Then there's this famous problem of evil passage from the Bhuridatta Jataka (although, to be fair, this is most likely a later addition that some date to the 13th century):
We see those rules enforced before our eyes,
None but the Brahmans offer sacrifice,
None but the Khattiya exercises sway,
The Vessas plough, the Suddas must obey.
These greedy liars propagate deceit,
And fools believe the fictions they repeat;
He who has eyes can see the sickening sight;
Why does not Brahma set his creatures right?
If his wide power no limits can restrain,
Why is his hand so rarely spread to bless?
Why are his creatures all condemned to pain?
Why does he not to all give happiness?
Why do fraud, lies, and ignorance prevail?
Why triumphs falsehood, truth and justice fail?
I count your Brahma one of the unjust among,
Who made a world in which to shelter wrong.
Those men are counted pure who only kill
Frogs, worms, bees, snakes or insects as they will,
These are your savage customs which I hate,
Such as Kamboja hordes might emulate.
If he who kills is counted innocent
And if the victim safe to heaven is sent,
Let Brahmans Brahmans kill so all were well
And those who listen to the words they tell.
At best, God would have be more like the impassive and impersonal God of Aristotle, existing outside of time and space, to find a place within Buddhist cosmology. Nevertheless, even in the earliest parts of the Pali Canon, there are references to devas or what we might call 'heavenly beings.' However, devas (literally 'radiant ones'), which are often seen as gods when taken literally, are simply non-human beings who are more powerful and long-lived than ordinary humans, and are by no means eternal, omnipresent, omnipotent, etc. But more importantly, they can also be viewed metaphorically as the indulgent and hedonistic aspects of our psychology (i.e., the parts that are addicted to sensual pleasures).
In addition, according to AN 3.61, the belief in a supreme being can be unskillful and interfere with Dhamma practice if it leads to the belief that everything a person experiences is due to such a supreme being, a denial of the efficacy of kamma (literally 'action') and a life of inaction:
Having approached the priests & contemplatives who hold that... 'Whatever a person experiences... is all caused by a supreme being's act of creation,' I said to them: 'Is it true that you hold that... "Whatever a person experiences... is all caused by a supreme being's act of creation?"' Thus asked by me, they admitted, 'Yes.' Then I said to them, 'Then in that case, a person is a killer of living beings because of a supreme being's act of creation. A person is a thief... unchaste... a liar... a divisive speaker... a harsh speaker... an idle chatterer... greedy... malicious... a holder of wrong views because of a supreme being's act of creation.' When one falls back on creation by a supreme being as being essential, monks, there is no desire, no effort [at the thought], 'This should be done. This shouldn't be done.' When one can't pin down as a truth or reality what should & shouldn't be done, one dwells bewildered & unprotected. One cannot righteously refer to oneself as a contemplative. This was my second righteous refutation of those priests & contemplatives who hold to such teachings, such views.
Furthermore, in relation to the four noble truths and the practice of the noble eightfold path, the matter of the existence of God is irrelevant and, soteriologically speaking, a distraction to be avoided. Of course, this doesn't mean that people can't believe in God and still practice the Dhamma, especially some of its more contemplative aspects, but it does mean that, at the very least, such views can negatively impact the practice when held inappropriately.
In my opinion, Buddhism has always been what we might call a type of 'transcendent psychology,' and it's only been relatively recently (at least in the West) that its more technical terms have been understood and translated in ways that make this clear. I think this shift is due in no small part to the decades of excellent scholarship that's been brought to bear on the texts and the religious-historical context in which they took shape. As I mentioned all the way back in my first post, regardless of how it's been popularized, at its core, Buddhism deals exclusively with one subject, that of human mental suffering. The Buddha himself made it clear that:
Both formerly and now, monks, I declare only stress and the cessation of stress.
That's not to say there aren't 'supernatural' concepts in Buddhism, or that local customs, deities and religious practices haven't found their way into Buddhism wherever it's been established. But rather than a pure system of thought or a strictly faith-based worship of the supernatural, a critical analysis of the earliest texts reveals a much more pragmatic and specialized method of mental training than most traditional Buddhists and Western converts realize—one that seeks to diminish and even eliminate suffering by radically changing the way the mind relates to experience.
Whatever else this radical transformation may open one up to, I can't say, but I suspect that Thanissaro Bhikkhu's right when he says that we're "not committing spiritual suicide." The allegory of the cave in Plato's Republic immediately comes to mind here, where he uses the image of the philosopher turning the soul (mind) away from the darkness of the visible realm (samsara) towards the light of the form of the Good (nibbana). So, from this perspective, being an atheist, or even a theist for that matter, doesn't preclude one from practicing Buddhism so long as one has an open mind and is willing to at least give some of these teachings a chance.