I typically like the most scientific ones rather than the touchly-feely ones. There was one about stock market crashes which I found really interesting . here it is http://www.ted.com/talks/didier_sornette_how_we_can_predict_...

Haven't kept up very well, so there might be more recent ones that best these, but from what I remember...

The funniest while still being somewhat interesting was Ze Frank. The most interesting while still being really funny was Sir Ken Robinson. Lessig's talk about Sousa was also pretty amazing.

<shameless_plug> Are we allowed to suggest our own? :) https://www.youtube.com/watch?v=MY3XWYr726I </shameless_plug>

I'll get my coat ...

If this is your favorite, of course ;)