It is no big news that Lawrence Lessig, founder of Creative Commons and professor at Havard Law School among other things, is a smart guy and a great speaker. In this 18 minute presentation, given at TEDx Bosten on July 29th 2010, he explains the idea of citizens working for society and themselves through self-organised action. He follows the big issues at hand in the US (and the world) today. One might not agree with all the points he makes (I actually do not) he still makes some interesting observations.
Besides the content of the speech itself this is a great example of how to give a gripping presentation.