Randy Pausch's Last Lecture. I had heard about this when featured on all the primetime news stories a few months back, but I actually just finished watching the lecture on youtube and it totally made me cry at the end.
Then I watched the ABC special on him and I cried some more.
Geez, I'm an emotional wreck over here!
Peep the videos below:
"Randy Pausch Last Lecture: Achieving Your Childhood Dreams"
EDIT: I figured I might as well post the video here for you to watch and enjoy. Take the time to watch it. It's over an hour long.