Partial List of Online University Lecture Sites
Lecture Fox: This site links to thousands of lectures in video, audio, and text formats, from top universities around the world.
Academic Earth: Previously covered here, this website appears to be growing into what may be come the go-to site for video lectures online.
Free Science and Video Lectures Online: This is a blog that covers a different subject area of online lecture videos in each post. The archives are extensive.
World Lecture Hall: This site contains a large searchable list of online lecture topics in a wide range of subjects.
Cosmolearning: Wide range of course topics particularly in science and computer science.
LearnersTV Nice selection of lectures, animations and notes on the sciences, engineering, computer science, medicine, and management. (added 7 Aug 09)
There are many more such sites available, and I will be mentioning more as I become more familiar with them. Also check out the Online education category below.
Video Lectures Net
Online Neuroscience Lectures
Theoretical Physics Talks and Conferences
101 Lectures on Open Source educational technologies
NPTEL: Engineering, Technology, and Computer Science course lectures from IIT
Khan Academy lectures on math, science, banking, and finance (added 6 Aug 09)
FreeVideoLectures.com (added 7 Aug 09)
http://www.lecturesarchive.com/5726.html (added 30 Oct 09)
Open Courseware Finder -- Expansive Search Engine (added 30 Oct 09)
Take Any Class for Free (added 30 Oct 09)
Update: You Tube Edu: This You Tube channel