The Astronomy Society of the Pacific has made many of the talks from their annual Silicon Valley Astronomy Lectures available for free on their website in the form of The Silicon Valley Astronomy Lectures Podcasts. There are lectures from the likes of David Grinspoon, Alex Filippenko, and Frank Drake.
There are videos of some of the lectures available for you iTunes users. Not sure why you need iTunes to watch free videos. Embrace the torrent.
Via: Bad Astronomy