Is there a site that provides online RAIM predictions for the US? I know
that Flight Service is supposed to be able to provide this, but it would
be nice to have another source.

A GNS 430/530 will provide it.

Yes, I should have added that I can get it from the receiver (our club
recently installed a GNS 430), but I 'm looking for a source I can use
during preflight.

Barry