... on the institution of marriage, I suggest going with this lengthy, thorough, and very good NRO interview, conducted by Kathryn Lopez, with Robert P. George, professor at Princeton and one of the foremost defenders of marriage. Highly recommended.
UPDATE (June 29, 2011): Also see canon lawyer Dr. Edward Peters' helpful post, "One demur to Robert George's excellent interview on marriage", on his "In the Light of the Law" blog. Also see his other new post, "A note on Gov. Cuomo's devotion to St. Thomas More".