Atheism is not a belief system. It is merely the lack of a belief in god. For the morality side there are several belief systems such as Humanism.
My personal beliefs are that there is no god, nothing supernatural, no magic, and no afterlife. The afterlife question is the one that I struggled with the most.
When you die, your body just dies. It stops working and decomposes just like any other life. Your brain is just contained in your body, you don't have an everlasting "soul". However, everything that you did during your life - everyone you talked to, saw, was seen by, actions you did, actions others did against you, even how much air you breathed d uring your life continue on. People that are still alive will continue on, altered by your influences. Your interactions with the environment have lasting impacts on the world. That is the afterlife. If you do good then your afterlife will be positive on everything else. If you do bad then you caused harm and people will have bad memories of you. That's the only "afterlife" that can be guaranteed, it's not dependant on anything else.
Treat others the way you want to be treated. This applies to almost any situation. Don't steal because you don't want to be stolen from. Don't hurt others because you don't want them to hurt you. Don't take away someone's freedom because you don't want them taking away yours. This can be perverted just like any religious claims though, but it works in most cases.
May 2010: Draw Muhammad Day with Mechanical Turk
City of Fullerton Invocations
June 23, 2007: Does God Exist? Debate
Rules good christians should live by
How to Kill God (external link)
Before the big bang? Don't know. What started the first life? Probably random chance. Evolution is clearly correct though. We so perfectly matched to our environment because we evolved to fit our environment perfectly. If we breathed helium instead of oxygen then the creationists would be proclaiming that breathing helium was the only perfect way to be created.