I have been using mythnettv for a long while to download and import videos directly into MythTV. I want to share the feeds I regularly watch with you. Just add the following links with mythnettv or if you like with mirobridge.

TED Talks: TED is famous for its lectures, known as TED Talks, which
originally focused on technology, entertainment and design, but have
now expanded in scope to a broad set of topics including science, arts,
politics, education, culture, business, global issues, technology and
development.

Pad Condell: Posts short monologues denouncing religion and lack of critical thinking.

Big Ideas: is a Canadian television series showcaseing public intellectual culture. The show features public lectures by acclaimed university educators and other distinguished guests.

Think Again: Lectures from tvo.

FORA.tv: Gathers the web’s largest collection of unmediated video drawn from live events, lectures, and debates at universities, think tanks and conferences.