If one were to rely on the Los Angeles Times for one's knowledge of Judaism (which, I am afraid, is the case for many Californians, including many Jews), one might assume that Jewish religious leaders enthusiastically oppose Proposition 8, the Protection of Marriage Amendment. Indeed, that is the position of the Board of Rabbis of Southern California, an organization that nominally is made up of rabbis from all Jewish denominations, but to which few Orthodox rabbis belong, and in which still fewer actively participate. It is dominated by the Reform, Conservative and Reconstructionist strains of Judaism, who dictate its policy pronouncements.
"Strains" is a particularly appropriate word in this context, because opposition to Prop. 8 strains traditional Jewish values on marriage beyond the breaking point.
For the view of authentic Torah Judaism on same-sex marriage, based on the written and oral Torah (as opposed to current "progressive" societal fashion), I strongly recommend a column entitled "Marriage Matters," written by Rabbi Avi Shafran, the Director of Public Affairs of Agudath Israel of America, which appears on Cross-Currents, a website that publishes the opinions and observations of a talented repertory company of knowledgable and articulate Orthodox Jewish writers. Rabbi Shafran notes that the rabbis of the Talmud deal explicitly with the subject of same-sex marriage, and "consider a society that 'writes marriage documents for men' to be endangering its very existence."
While Augudath Israel of America is an advocate for the viewpoint of "haredi" Judaism, centered in the yeshiva and Chasidic world, on this issue Rabbi Shafran's column states the position of the entire spectrum of Orthodox Judaism, including the centrist Union of Orthodox Jewish Congregations of America.