Professor Robin Wilson of Gresham College has delivered a number of outstanding lectures, mostly about historical mathematical subjects, that are available from the College's web-site. The lectures are viewable by Real Player and there are transcriptions in PDF format and lecture notes available. The lectures I've watched are a half hour long but I don't know if that's the case for all of them.
There are 30 lectures available from Professor Wilson. Topics include:
- Much ado about zero
- Prime-time mathematics
- How hard is a hard problem?
- Who invented algebra?
- Who invented the calculus? and other 17th century topics
- Wallpaper patterns and buckyballs
Two that I've particularly enjoyed are "Problems with schoolgirls" and "Who invented algebra?"
Enjoy the lectures and share a comment about the ones you like.