The Massachusetts Institute of Technology OpenCourseWare effort has been offering free lecture notes, exams, and other resources from more than 1800 courses per its website. Some of their courses offer a substantial amount of video and audio content. I remember stumbling across this resource via my employer's intranet about a year ago. Frankly speaking, I didn't think the concept would go very far because you couldn’t earn credit…
Well, I was wrong. It’s catching fire and over 100 universities worldwide have setup similar models and some are top tier schools such as Johns Hopkins and Tufts.
I was searching for a good UNIX course but I haven't found one yet. Surprisingly, it appears MIT’s Linear Algebra course is quite popular with the OpenCourseWare community.
By the way, I don't have any affiliation with OCW or any of the higher learning institutions mentioned.
Added later:
UC Irvine OCWNotre Dame OCW
Utah State OCW
Osaka OCW
Japan OCW Consortium