Carolyn Porco: Fly me to the moons of Saturn.
Richard Dawkins: An atheist's call to arms and The universe is queerer than we can suppose
Tierney Thys: Swim with giant sunfish in the open ocean
I also enjoyed Jennifer Lin: Magical improv from 14-year-old pianist (esp. the "improvisation" section), Julia Sweeney: "Letting Go of God", Rives: "If I controlled the Internet", and an extremely interesting Jonathan Harris: The Web's secret stories for those of us who love gorgeous interfaces/ideas/presentations.
Take a look at TED - it's a good way to spend some of your time.
Added Nov 9th: Larry Lessig: How creativity is being strangled by the law