Just in time for my courts unit, the US Supreme Court accepted two cases on gay marriage. Above is a succinct new clip detailing both of them. Here is the NYTimes article and the place to go for Supreme Court cases is SCOTUS blog which has an analysis here. Here also is the US Supreme Court page on Holingsworth v. Perry where your students can see such terms writ of certiorari and see the amici groups. They key, I believe, that this case has been lead by the plaintiff's high profile lawyer Theodore Olson who was George W. Bush's solicitor general and David Boies - a noted Democrat and the lead lawyer for the US government case against Microsoft. After leaving government he took on the case despite his conservative brethren's dislike of the idea. Here is a history of the case to date which shows how the names of cases change and how the case wound its way to the highest court in the land.
Here is the page for the US v. Windsor case. Both the links come from SCOTUS Blog and have links to all the other amici briefs.