As I understand it, the homosexual marriage movement is primarily, but not entirely, a pursuit for the same legal status as heterosexual marriage. (I use that caveat, "primarily", because some domestic partner laws seem to be "marriage" in all but name, in spite of which some still agitate for that specific expression.) When I began thinking about this, a question arose in my mind: is marriage primarily a religious or a secular status? Presently, there is an overlap between the two domains. Clergy can conduct a marriage ceremony for any and all they desire, according to the tenets of their own faith, but the law won't recognize any of them unless a marriage license - a secular document - is granted, signed and returned to the government. In the case of a marriage ceremony conducted by a Justice of the Peace, or other non-religious authority (e.g. ship's captain), we have become accustomed to referring to the couple's status as "married", even though some later have an actual religious ceremony.
So perhaps it's time to officially separate the legal contractual status from the religious status. This would not require much change in the religious domain, as the various churches could retain their current practices, including the right to refuse holding a marriage ceremony if such would violate that church's tenets. On the legal side, however, some term should be recognized to infer a contractual status between two individuals, a status recognized by the states - yes, all of them - as being accorded the privileges of a married couple.
(This should not imply carte blanche for same-sex couples, by the way. Some of the arguments opposing same-sex unions are well-taken - legal recognition of polygamy and polyamory would have too jarring an impact on society, and anti-incest restrictions should still be vigorously enforced, for various reasons having to do mostly with the psychology of such relationships.)