I just found out Stanford and Apple have put a whole bunch of audio content on the iTunes music store for free. You can download lectures by faculty, speeches by guest speakers, and much more. There's a lot of interesting content to listen to. Make sure you click on all the tabs at each page (for example, "Human Health" and "Environment" under "Global Issues").

Click here to go to the iTMS page

Or click here so see a list of some of the stuff I've already downloaded

Update: I guess it's all official now, with more audio and video content coming! Click here for the content