Internet Infidels (infidels.org) is a website that promotes metaphysical naturalism, which they define as the hypothesis that the natural world is a closed system. The site is one of the oldest on the Internet promoting atheism and related subjects, and is a classic in the genre.
The site contains material describing and defining concepts such as atheism, agnosticism, naturalism and secular humanism. In addition to that, it also contains material arguing that the beliefs of the world's major religions are false. They also have material on paranormal woo like near death experiences.