FFRF = Freedom From Religion Foundation. They are very aggressive in separation of church and state. So is the ACLU, actually. Unfortunately, it's the "privacy" part that gets lost, on both sides - many atheists want believers to acknowledge the irrationality of faith, and many believers want religion in hthe public sphere.

As you can probably tell, I'm more in the former camp than the latter, but if believers WOULD keep their faith private, I might not be. Except for the children, of course. Kids' right to a full education way, way outweighs any parental privilege of freedom of religion.