I'm particularly fond of Steven Levitt after reading Freakonomics. I enjoyed his talk on the pointlessness of mandating car seats for children and what should really be done to improve their safety:

http://www.ted.com/index.php/talks/steven_levitt_on_child_ca...

I also like the SeaDragon/Photosynth demo (along with various other talks that have come from Microsoft Research)

http://www.ted.com/index.php/talks/blaise_aguera_y_arcas_dem...