It used to be that I had to rely on the Bush v. Gore case to let my students hear oral arguments. Now in two days we have two oral arguments I can choose from that my students will be interested in hearing. The nice thing about the one above is that you get a picture of the justice who is speaking. I put Hollingsworth v. Perry on top and US v. Windsor underneath it. Here are both today's and yesterday's for both transcript as well as the oral arguments.
The top item on this blog is from Oyez which is a tremendous site that has every Supreme Court case and everyone oral argument that has been released in audio format. I use it (and Wikipedia) when I want my students to look up court cases.