I've heard that all but 2 of the current SCOTUS justices are Catholic.
If true, then Scalia is the only one I know to be a consistent Catholic. (Thomas might be one of the non-Catholics, so that leaves only Rehnquist as the only other potentially consistent Catholic out of 7....if the numbers I've cited are accurate.)
I believe that Clarence Thomas is Catholic.
From:
http://www.adherents.com/adh_sc.html
William H. Rehnquist Lutheran
Stephen G. Breyer Jewish
Ruth Bader Ginsburg Jewish
Anthony M. Kennedy Catholic
Sandra Day O'Connor Episcopalian
Antonin Scalia Catholic
David H. Souter Episcopalian
John Paul Stevens Protestant
Clarence Thomas Catholic