Dr. Mark Thornton from the Mises Institute spoke to the Auburn University Libertarians earlier this month. He gave a 30 minute "Introduction to Libertarianism", starting with his introduction to the philosophy and party as a college student.
This would be great to pass along to a friend who leans Libertarian, but doesn't quite get it yet. It's very easy to listen to. Dr. Thornton does a great job relating Libertarian ideals to current situations. AUL has a link to the mp3 on their news page, or you can go to:
http://www.mises.org/multimedia/mp3/Thornton-01-19-2006.mp3
The Mises Institute also has many of their past programs & lectures available on their media page.