I knew that Ellison used the Qu'ran...and recall that he was widely reviled as being unamerican for doing so, despite the theoretical separation of church and state.

I'd prefer that nothing be used also, or maybe just swear on the Constitution, since that is what our elected reps are supposed to be upholding. But that could be viewed as me imposing my personal philosophy (leaning toward secular humanism) on others, I suppose.