I'm an atheist. I was born in a family where religion was given very little importance. My mother's relatives baptized me as Orthodox Christian (I was born in what used to be USSR) more for the sake of tradition than anything, and she tried guilting me into wearing a cross on my neck for years, but I ended up ditching it. On the other hand, we had a ton of litterature, including books on lots of different religions, and could basically make our choices ourselves.
I clearly remember, at the age of, like 6 or 7, having a children's edition of the Bible and a book called "Encyclopedia for children" which basically laid out science in a lot of fields (including the creation of Earth, evolution etc) in a manner accessible to kids. I tried reading both, and, frankly, the latter made all the sense in the world to me, while the former did none.
With time I also became somewhat of a nihilist. For those who don't know what it is, I basically believe that everything, including our existance, is completely meaningless in the grand scheme of things. While a lot of people find that depressing, I see it more as a positive thing, as it takes a lot of pressure off. On the other hand, I think that, since there's no higher power to judge us upon death, the only judges we have are other people who are as short-lived as we are, and while I don't think we were handed rules from above, it doesn't mean we don't need empathy, decency, respect...
At the end of the day, I can say that my philosophy has only two commandments: live your life the way it makes the most sense to you because it's the only life you've got, and never and in any manner get in the way of other people's doing the same.