In a meeting with Embassy staff at the U.S. Embassy in London, Secretary of State John Kerry has announced that the Department of State would treat same-sex married couples as equal to other married couples.  Kerry stated:   

If you are the spouse of a U.S. citizen, your visa application will be treated equally. If you are the spouse of a non-citizen, your visa application will be treated equally. And if you are in a country that doesn’t recognize your same-sex marriage, then your visa application will still be treated equally at every single one of our 222 visa processing centers around the world.  Now, as long as a marriage has been performed in a jurisdiction that recognizes it so that it is legal, then that marriage is valid under U.S. immigration laws, and every married couple will be treated exactly the same.  

The Department of State also issued guidance on this issue in the form of Frequently Asked Questions (FAQs), which specify that so long as the marriage was valid in the state, country or jurisdiction where it took place, it is valid for U.S. immigration purposes.  Therefore, same-sex spouses will qualify for dependent nonimmigrant visas, immediate relative and family-based immigrant visas, derivative permanent resident status, and any other benefits previously available only to opposite-sex married couples.  The Department of State clarified that civil unions and domestic partnerships do not qualify at this time, only legal marriages.  The complete set of FAQs can be found at: http://travel.state.gov/visa/frvi/frvi_6036.html.