As far as the Founding Fathers stuff goes, keep in mind the following:
- There's no mention of Jesus Christ anywhere in the Constitution or Declaration of Independence
- The Constitution does not mention God AT ALL
- The Declaration of Independence mentions God three times - the first as "the laws of nature and nature's God," the second as "endowed by their Creator with certain inalienable rights." It also mentions "Divine Providence," which could be considered a reference to God.
- The 85 essays of the Federalist Papers only mention God twice, both by the same author (Hamilton), both in the "God only knows" sense
- "In God we Trust" didn't appear on coins until after the Civil War
- "Under God" wasn't part of the Pledge of Allegiance until 1954
- Ben Franklin was a deist
- Tom Paine was also a deist, although he was frequently labeled an atheist due to his criticisms of most religions
- Thomas Jefferson proclaimed himself a Christian, but he dismissed the foundation of the religion (virgin birth, the miracles, etc.) as "the fable." Jefferson simply admired the moral teachings of Jesus; he didn't buy into the mystical portion of the religion. Today that would pretty much make him an outcast in most Christian churches. Jefferson went on to found the University of Virginia, at which he banned the teaching of theology.
- Washington and Madison were basically agnostic; Washington spoke of God in non-denominational terms such as "Great Author" and "Almighty Being." Madison wrote of the negative actions individuals have taken in the name of Christianity.
The Founding Fathers all seem to have had their own concepts of the existence of a God. But to say they were all Christians, especially in the sense we consider Christianity today, is false.
Finally, I'd point out the Treaty of Barbary, ratified unanimously in 1797, which contained the phrase: As the Government of the United States...is not in any sense founded on the Christian religion. Of course this was not the point of the Treaty, but does anyone think phrasing like this would have any chance of being accepted today?
