Here is a link to the College of DuPage History of Photography classes taught by Jeff Curto. The podcasts are free. You can subscribe to them in iTunes. The podcasts are quite good, and they area a valuable resource.
iTunes lists several semesters going back a few years. Each of the semesters cover the same material, but the older semesters used a QuickTime technology that embedded visual content right into the podcasts. This is helpful if viewing on a mobile device like an iPad or iPod. Later semesters have the visual content available on the History of Photography Web page.
My Nikonians Gallery