1. TED - Ideas Worth Spreading (www.ted.com)
The annual conference brings together wide variety of thinkers and doers.  There are talks on several different topics. Content include science, business, arts and much more.

2. FORA.tv - The World is Thinking (www.fora.tv)
FORA.tv has the largest collection of video drawn from live events, lectures, and debates from world’s top universities, think tanks and conferences. Topics include Politics, Science, Technology, Economy and more.

3. Bigthink - Get to know (www.bigthink.com)
Bigthink is another site with wide array of topics from different experts

4. MIT World - Distributed Intelligence (mitworld.mit.edu)
MIT world has over 500 on demand videos of public events at MIT.

5. Research Channel (www.researchchannel.com)
More than 3500 videos in Arts, Sciences, Business, Health and so much more.

Let me know below in the comments if you have any more.