I am writing (under my real name) a thin book called: The Church of the Undammed - Beyond Faith that lays out my atheist philosophy on purpose, compassion, ethics, and the value of this life, the fallacies of uncritical thinking vis-a-vis 'there has to be a god', as well as my observations of and objections to the negative effects of religion and faith on our ability to achieve the best possible value within the context of the brief and entirely temporary existence we are lucky enough to get to take part in.
I will probably make this available as a pdf on AN as soon as I get to a final draft.
Sorry, but an Atheist Manifesto scares me. Will we have to sign it, swear to/by it, fit our thinking into it, behave/believe according to it...and will we split off into factions based on different interpretations of it, bicker amongst ourselves about who has the "right" interpretation of it, come to blows when we cannot agree about it...
Why do we need some specific codified document? Why is "I do not believe in, need, or want a God" not enough?
Fight conformity. Question everything. Think for yourself.