Answer
The best site I would recommend to start and to keep as a daily blog read is Austin Cline's http://atheism.about.com/. This is a great place to start for all the basics in regards to atheism, philosophy, religion in general and current events that relate to these subject matters. There are other great sites but this is the best starting point.
There are no principles of atheism, any site one might mention could only have to do with humanism, atheism is not a belief system, it is a lack of belief, god is a metaphor for the great mystery of the existence of the world and of your own being, the religious concretise the term, getting stuck with the metaphor/idol if you cannot look passed this then the metaphor/god is in your way. The only reason to organize is to halt the polictial ambitions of the religious as the try to interpret the modern world through a two thousand year old text of two thousand year old hear say. You do not need to study atheism, if you do not believe that is what you are, for all intent and purpose-no basics, if you do not believe you are there.
Atheism is in fact merely a descriptive term used to denote an absence of belief in a supernatural god. Many "atheists" contest the validity of labelling a group by their lack of belief from the viewpoint that no one is labelled as a "non-believer in unicorns" or a "non-believer in pots of gold at the end of rainbows."
The reason that the term "atheism" does exist is that religious believers comprise a large majority worldwide. A simple term to differentiate a non-believer as such is naturally needed, thus "atheism."
A common misconception among religious believers is that a lack of belief in a higher moral power puts a non-believer in a position of vulnerability with regard to moral resolve. For instance, if there is no reckoning with an ultimate moral authority at the end of life, what would prevent people from robbing banks or murdering if they knew beyond the shadow of a doubt that they could pull it off without getting caught.
The following websites address this and other commonly cited misgivings about secular humanism and atheism.
http://www.reasonproject.org/
http://richarddawkins.net/
http://richarddawkinsfoundation.org/
http://the-brights.net/
http://outcampaign.org/
http://www.positiveatheism.org/