TED is:

… a small nonprofit devoted to Ideas Worth Spreading. It started out (in 1984) as a conference bringing together people from three worlds: Technology, Entertainment, Design.

If you like smart stuff you will love TED Talks. I have watched dozens of these over the last couple of years and have never been disappointed. I tend to focus on tech or UI related talks like anything from Hans Rosling (he is a fantastic presenter, too):

Another one of my favorites is an incredible demo of some tech coming out of Microsoft, presented by Blaise Aguera y Arcas:

There are also random ones that don’t seem to have as much of a point to them but are utterly hilarious, like this presentation by Ze Frank:

Tip: browse the presentations with the filters on the left to find some of the best talks. Enjoy.