Part of the reason for my cavalier response previously is that I found some of the implications of what I thought your question was...a bit unsettling. It seemed to me you were saying that you could easily write your "antagonistic/evil" atheist because clearly thatís the core of atheism:
But you were having trouble writing your "good/peaceful" atheist because nothing in the tenets of atheism offered any encouragement to be good.
Hopefully one of the things youíll get from further investigation is that there are no tenets of atheism. There are, however, various schools of philosophical thought that provide all manner of rationale for being "good" and "peaceful". There are also legal and social encouragements aplenty.
Iím a big fan of Sam Harris. Even when I disagree with him, I find his arguments framed so eloquently that I enjoy hearing what he has to say. And so dreamy...oops, had to wipe the drool off my keyboard (I kid!). His book The Moral Landscape addresses your question quite directly and it isnít as pedantic as a lot of Dawkins (tho it isnít as funny as a lot of Hitchens).