While atheism is not a philosophy as such, the reasons that one has for being one (mainly, the rejection of those beliefs for which there is no evidence) necessarily lead to certain consequences. Collected together, this set of results may look like a philosophy, but is not really. It is merely the playing out of the consequences of a scientific approach to every aspect of life.
For example, the same arguments that atheists use to reject the existence of god also lead them to the rejection of an afterlife. This has profound consequences for the way one lives and how one relates to others. For me, the fact that this life is all there is makes more imperative the importance of everyone being able to make the best of the one life they have. There is no heavenly compensation to satisfy the yearnings of people who are suffering here and now. All people have a right to, at minimum, adequate food, shelter, clothing, and health care, and there is no excuse for societies not being structured to provide them with those necessities.
Similarly, all people have a right to seek happiness wherever they can and with whomever they wish as long as they are not harming others. Hence gays, lesbians, and transgendered people are entitled to every right enjoyed by others, and atheists oppose objections to their behavior based on reasons like “god considers such acts sinful and they will go to hell” or because some religious text forbids it. (It is only such kinds of reasoning that is rejected. There may be atheists who disapprove of homosexuality on other grounds, such as that it is ‘not natural’ (whatever that may mean), but that is a different issue not involving religion.)
The same reasons that lead atheists to reject god also lead them to reject the idea of an independent soul that can survive the body. The problems of reconciling the idea of a non-material soul (or mind) interacting with the material brain and body are just as great as trying to figure out how a non-material god interacts with the material world. So I would argue that another corollary of being an atheist is to reject the idea of having a soul that can exist independently of the body. One can retain a concept of a ‘soul’ as long as it is merely a euphemism for the mind, a creature of the brain that ceases to exist when a person dies.
The idea that there is no god out there setting the standards of ethical and moral behavior also means that, rather than fighting to see which version of religious morality and behavior should prevail, atheists believe that we have to figure out what are the common bases on which we can live with one another in peace and justice in the world.
So in other words, the fact that atheism correlates with rejection of an afterlife and souls and religious text-based moral and ethical values means that the whole package has the trappings of a philosophy. But actually they are the almost independent consequences of having a philosophical naturalism philosophy that uses a scientific approach (empirical evidence and logical reasoning) to determine which beliefs are worthy of acceptance and which are not.
POST SCRIPT: Michael Moore on Oprah
The video of Oprah Winfrey interviewing Michael Moore on her show about his new film Sicko seems to suggest that she is going to take up the cause of a a single-payer universal health care system. (See the Post Script to this post for a preview and a clip from the film.)
If she does so, this could be a big step towards establishing such a system because the platform she has gives her a formidable ability to mobilize public opinion.