ArsTechnica reports on Google Techtalks for the chronically curious.
The talks are available through Google Video:
(I've also heard that Google has book talks, I don't know if this is the same thing as the tech talks.)
Ars also lists a bunch of other sources of "broadly academic" videos:
- PBS Scientific American Frontiers
- Vega Science Trust - Reflections on Science
- Mathematical Sciences Research Institute - VMath Video Archive
- Exploratorium Webcasts and Archive
- JPL 2001 von Kármán Lecture Series
To that list I would add the seminars available from the Canadian Perimeter Institute for Theoretical Physics, the streaming videos are listed at https://streamer.perimeterinstitute.ca/mediasite/viewer
For general audiences, you may want to click on the Public Lecture Series listed on the above page.
Their online setup shows the presenter and the slides from the presentation side-by-side, which is nice.
Upcoming public lectures are listed at https://www.perimeterinstitute.ca/activities/community/generalpublic/publiclectures.php