here is the link for a very useful resourse - TED ideas worth spreading - http://www.ted.com/themes.
TED makes the best talks and performances from TED and partners available to the world, for free. More than 450 TEDTalks are now available, with more added each week. All of the talks feature closed captions in English, and many feature subtitles in various languages. These videos are released under a Creative Commons license, so they can be freely shared and reposted.