Expanded Version : Are Buddhists Atheists?
According to online dictionary m-w.com, an atheist is one who believes that there is no deity and a deity is the rank or essential nature of a god/ a god or goddess/ one exalted or revered as supremely good or powerful.
Many theists, be they monotheists (those who believe in one God) or polytheists (those who believe in multiple gods), see Buddhists as atheists - because there is no god as the central refuge in its teachings. But how true is this?
Buddhists take refuge in the Triple Gem (Three Jewels) - the Buddhas (there are countless Buddhas), the Dharma (the Buddhas' teachings that lead to enlightenment), and the Sangha (the community of Dharma practitioners, which includes humans and gods, who have attained at least stream-entry, which is the first spiritual fruit on the path to enlightenment). It is important to note that the Sangha consists of some gods (devas) too, of whom are celestial (heavenly) Bodhisattvas such as the well known Avalokiteshvara (Guanyin) Bodhisattva. Bodhisattvas can manifest as some gods out of skilful means too, though Bodhisattvas are never manifestations of ordinary gods. In this sense, Buddhists do take refuge in some, but not all gods, as not all are of the Sangha. However, many gods take refuge in the Triple Gem.
Traditionally, Buddhists take refuge in all three aspects of the Triple Gem collectively. This is true, other than the Buddha's several first disciples, who took refuge only in the Buddha and the Dharma he taught - in the absence of the Sangha, that was formed shortly after - at the end of the first sermon. Yet in a way, the Buddha himself was already the perfect embodiment of all three aspects of the Triple Gem.
The (historical) Buddha as a spiritual refuge is obviously not a god or a creator God (which Buddhism does not subscribes to - as it believes we collectively create and re-create the world continually through karma). But one of the traditional titles of the Buddha is Teacher of humans and gods. He declared himself to be wholly spiritually purified and perfected, to be faultless, to be one who had transcended both human and godly limitations. In the spiritual and physical sense, every Buddha is equally supreme to each other, and are thus God-like - in a very loose sense of the word.
Are Buddhas divine? According to the same dictionary, divine refers to that of, relating to, or proceeding directly from God or a god/ being a deity/ directed to a deity/ supremely good. We need to note that the divine is usually related to the godly only. As the Buddha clearly said he is not an incarnation of any god or any god's messenger, and that he had transcended all gods, he is nevertheless divine as he is supremely good. The goodness of the Buddha is so supreme that it is called pure, which transcends both worldly and godly goodness.
So, are Buddhist really atheists, monotheists or polytheists? There is no clear-cut answer, since many use these terms differently. A complete answer to the question would resemble one of at least this length. However, Buddhism explains how theism evolved through history, and it is from this that we can see how Buddhism sees itself in comparison. In the ancient days of lack in understanding of nature, when humans experienced the wrath of nature, they instinctively assumed there to be gods of nature who were angry at them. Thus arose belief in earth gods (who create earthquakes), mountain gods (who create landslides), river gods (who create floods), lightning gods (who create lightning storms)... This is probably birth of polytheism. Some time later, it occured to humans that these myriad gods should be under the control of a supreme God who created and governs them, without which there would be total chaos. This is the birth of monotheism.
With the coming of Buddhism and its above understanding, none of the gods or God were taken as spiritual refuges, as the Buddha's complete awakening to the reality of life, the universe and everything clarified the earlier (mis)understanding of the nature of gods. But this is not to say no gods exist at all. In fact, in Buddhist cosmology, there are 26 intricately defined heavenly planes among its 31 planes of existence. The inhabitants of the heavens are of course, gods. And anyone who had created sufficient good karma can be reborn as a god, though a godly rebirth is not Buddhism's final aim. Its final aim is to urge all to become Buddhas - ones who have realised total freedom from the rounds of life and death.
It is interesting to note that in the Buddhist scriptures, there is a god described, with whom the Buddha interacted with, who had mistaken himself to have created the universe. This god invited the Buddha to teach after his enlightenment too. (For the sake of religious harmony, it would not be appropriate to claim or argue if this god/God is that of any other religion.) As described above, according to Buddhism, the rise of a religion which is not god-centric is seen as part of the process of the evolution of religion. The Buddha taught that, given enough efforts of spiritual cultivation, every single being can become spiritually evolved (be it in this life or another) to become perfect like him in compassion and wisdom. His goal was to teach the path to True Happiness for all beings, which is synonymous with the attainment of Enlightenment, which is the realisation of the truth of all things.
Atheism is also often lumped together with nihilism, which is in turn related to the total lack of morals. Not that Buddhists are atheist in the strictest sense of the word (as explained above), if one examines the Buddhist code of ethics, one will discover that Buddhism has perhaps one of the world's most comprehensive and compassionate moral system, which even takes into consideration of plants and the smallest sentient beings (eg. insects). Buddhism is incredibly conscious not only about human welfare in terms of promoting anti-sexism, anti-racism, anti-casteism, anti-speciesism, anti-dogmatism, anti-religious intolerance... it is also mindful of ecological and animal welfare. Thus is the first impression of the Buddha for many that of the embodiment of all-rounded compassion and wisdom.