Awesome Operating System lecture

UC Berkeley has its Operating Systems (OS) course lectures available online freely. I found them very lucid and helpful.

Here is the link:
http://academicearth.org/courses/operating-systems-and-system-programming

NB: http://academicearth.org/ in general has really good lectures. I also saw the Psychology lectures by Paul Bloom at Yale. He is a very good animated speaker. Check it out at http://academicearth.org/courses/introduction-to-psychology