I've been lucky to see a number of interesting talks and I figured I might as well point out a few they you can be lucky enough to see too:
How to survive a Robot Uprising -- hearing him talk was actually funnier than reading the book.
DNA and the Brain -- A talk about autism by James Watson of Watson & Crick.
An Inconvenient Truth -- Al Gore's talk about global warming (you'll have to go to a theater to see this one)
Does all this linking to Google video make me a company shill?