MIT offers Open Courseware, "free lecture notes, exams and videos" from MIT professors. Not all listed courses offer usable materials--many are just syllabi or reading lists; however, some provide lectures notes, audio lectures or more. Each listing shows icons of what content the course makes available, which is useful.
TechCrunch calls Academic Earth the "Hulu for education," and they're not wrong. Providing video content on topics ranging from literary history to astrophysics to politics, Academic Earth's site is searchable by topic, university or professor.
Moreover, the content comes from top-notch universities: Harvard, Yale, Stanford and Berkeley, just to name a few. Here's a selection from a series of lectures by Michael Sandel on "Justice: What's the Right Thing To Do?"
Watch it on Academic Earth