I just read a series of 10 blog posts by Steven D. Greydanus on the question of the redefinition of marriage. It is the best comprehensive treatment of the subject I have seen, and although for the blog world it is a long series, it's actually very concise considering all it contains.
Everyone involved in the current debates on marriage should read this. For non-Christians, they would likely see that the various Christian teachings on marriage and sexual morals form a cohesive whole that is ordered for the common good. For many Christians, they would also benefit from seeing the connections between contraception, divorce, abortion, and gay marriage. Often these topics are argued in isolation, but Greydanus shows how a "contraceptive mentality" is the root of them all. Even those who are familiar with the arguments Greydanus employs would likely benefit from seeing them presented in such a comprehensive, balanced, compassionate, and concise manner.