Maggie Gallagher makes one of the most thoughtful cases for Proposition 8 (and thus, against gay marriage) I think I've ever encountered. It's summary text is as follows:
Marriage between a man and a woman is rooted in our nature--''in biology, not bigotry''--sex between men and women makes babies, society needs babies, and babies need a father as well as a mother. But the proponents of same-sex marriage want the government to declare in law that there is no difference between same-sex and opposite-sex unions, and anyone who thinks otherwise is promoting bigotry. This will have major ramifications for those who believe in marriage in the traditional sense--especially religious citizens and organizations.
Finally, Evangelical Outpost presents an argument in favor of Proposition 8 along with a counter argument in reply. Yay for discourse.