God is Imaginary offers a series of proofs (50 of them) and for many of them, the site also offers common Christian rationalizations and rebuttals. Everything on God is Imaginary is written far better than anything I've written here, and there is an excellent forum (which I just joined).
Why I am an Atheist at ministerturnedatheist.org. Many, many atheists are not only former Christians, but former ministers. The reverse occurs infrequently enough to be worth noting. This one man's personal website is touching and, to me, inspiring (almost in a religious sense... heh).
Half Sigma's tag line is: The new politics of common sense. Neither Republican, Democratic, nor Libertarian. Even though it isn't, technically, about atheism or religion specifically, I include it here because of how it includes posts showcasing the religious extremism's detrimental behavior as an issue separate from party affiliation or identifications with conservatism or liberalism. This blog is, as it purports to be, very even-handed. It is also very much worth your time.