Harvard posts all of the major lectures they host in video format on a site called Harvard@Home, which allows those of us who cannot afford (or putzed around too much early in life) to attend an Ivy League school a chance to check out some of the great presenters that have spoken there.
Here are a couple of notable programs:
Changing Habitats... Vanishing Species: E.O. Wilson always has something good to say for those willing to listen, and in his portion of the presentation, he elaborates points made in The Future of Life, including habitat loss and extinction.
Evolutionary Dynamics: "In this lecture, Professor Nowak discusses recent and fascinating advances in our understanding of evolutionary dynamics and its application to genes, quasispecies, games, cooperative behavior, and human language."
State of the Global Environment: Another educated plea to listen to climatologists and finally make regulated steps toward conservation and energy alternatives.