A month or so ago someone asked me about gay marriage and the US Constitution. Following up on this issue, I suggest reading a recent case, Wolf v. Walker in which a Wisconsin federal court held that a ban on same-sex marriage was unconstitutional. Below is a video I have on YouTube discussing some issues in the case.
If you are studying US law you will find the case interesting for a number of reasons. First, the court decided to apply the intermediate scrutiny test to the Wisconsin law and state constitutional amendment which forbade marriage between anyone other than a man and a woman. The Court scrutinized the ban under both the Due Process and the Equal Protection Clauses.
The bulk of the court's analysis was as to whether banning same-sex marriage was so necessary to achieving an important government purpose that a person's fundamental right to marriage should be denied. The Court held that defendants failed to meet their burden.
For non-US students I think you may find interesting the Court's rejection of Wisconsin's arguments based on federalism and democracy. Among other things, defendants argued that if the people of Wisconsin supported a ban on gay marriage then a court should not interfere. The Court explained that principles of democracy or federalism do not trump the United States Constitution. Just as the people of a state may not constitutionally ban interracial marriage, banning same-sex marriage violates the US Constitution.
This was a district court decision and any appeal will go to the Seventh Circuit Court of Appeals.