To cite a TED Talk, TED recommends using APA Style for video Weblog posts:

Author. (Year, Month Date). Title [Video file]. Retrieved from URL

For example:
Sandberg, S. (2010, December 21). Sheryl Sandberg: Why we have too few women leaders [Video file]. Retrieved from http://www.ted.com/talks/sheryl_sandberg_why_we_have_too_few_women_leaders.html