Yale Professor Paul Bloom describes the important research on happiness in this lecture.
Another great talk by Paul Bloom (he also has a great free video lecture series on psychology)
Jason Fried makes a lot of great points on why the office is a productivity killer.
Gary Vaynerchuk on following your passion.
Scott Berkun is an excellent speaker (he also wrote Confessions of a Public Speaker)
Simon Sinek explains that people don’t buy what you do, they buy why you do it.