You know what, this is old, but I heard about it again and realized Scalia is sort of scary. From a dissent in the Kentucky ten commandments case.
"If religion in the public forum had to be entirely nondenominational, there could be no religion in the public forum at all. One cannot say the word "God," or "the Almighty," one cannot offer public supplication or thanksgiving, without contradicting the beliefs of some people that there are many gods, or that God or the gods pay no attention to human affairs. With respect to public acknowledgment of religious belief, it is entirely clear from our nation's historical practices that the Establishment Clause permits this disregard of polytheists and believers in unconcerned deities, just as it permits the disregard of devout atheists. The Thanksgiving Proclamation issued by George Washington at the instance of the First Congress was scrupulously nondenominational—but it was monotheistic.
Historical practices thus demonstrate that there is a distance between the acknowledgment of a single Creator and the establishment of a religion. The three most popular religions in the United States, Christianity, Judaism, and Islam—which combined account for 97.7 percent of all believers—are monotheistic. All of them, moreover (Islam included), believe that the Ten Commandments were given by God to Moses, and are divine prescriptions for a virtuous life. Publicly honoring the Ten Commandments is thus indistinguishable, insofar as discriminating against other religions is concerned, from publicly honoring God. Both practices are recognized across such a broad and diverse range of the population—from Christians to Muslims—that they cannot be reasonably understood as a government endorsement of a particular religious viewpoint.
I got it from [link]
The gist seems to be that it's okay to disregard atheists and any religion without Moses.