Well, not exactly. But the Harvard Extension School (2010, 2009, 2008) allows nonpaying online students to eavesdrop on the first few lectures of many of its courses. At the website you’ll see a long list of courses. Click on the “website” link of any course of interest, and in many cases you will be allowed to view the first few lectures.
Justice course from Harvard
Harvard Extension on iTunesU
More Harvard University for free
Yet more Harvard for free
Harvard Extension: “We still give free samples.”