Elder Bruce C. Hafen spoke at the World Congress on Families in May of this year. Here is a link to his talk.
I include this in part because some people have asked what some of my more "non-religious" concerns are with gay marriage. This talk reflects some of them. (For example, note his extensive comments about the problems that have (and continue to) come as individual rights are put before the welfare of society as a whole; the concerns about less-than-ideal situations for children (where the ideal is to be raised by biological parents); and the potential threat to democratic society if marriage is undermined (although my concerns regarding democracy take a different road than his).)
While I realize that some will want to take issue with some of his points (I think I can predict which ones will get the most reaction), I think he makes a good case for leaving marriage as it has always been defined: between a man and a woman.