TED Talks - 18 minute Lectures on the Great Issues from Great Thinkers

Physics and Astrophysics
Martin Rees - Astrophysicist: Is this our Final Century?
Peter Ward - On Earth's Mass Extinctions
David Deutsch - Our Place in the Cosmos
Murray Gell-Mann - On Beauty and Truth in Fundamental Physics

Climate
Dave Roberts - Climate Change is Simple

Science and PseudoScience, Perception, Reality
James Randi: Homeopathy, Quackery, and Fraud
Michael Shermer - How Pseudoscience purveyors work
The Optimism Bias

Society
Jared Diamond - Why Societies Collapse
Ken Robinson - Schools Kill Creativity
Alex Steffan - On a Sustainable Future
Ron Finley - Guerilla Gardening