Where can you find over 1,500 lectures from some of the top universities in the nation? http://www.academicearth.com. 

Academic Earth does not however produce any content.  Just like wikipedia, youtube, facebook and a host of other services have leveraged user generated content, Academic Earth is hoping to do the same for college lectures.  Academic Earth’s,  ”goal is to bring the best content together in one place and create an environment in which that content is remarkably easy to use and where user contributions make existing content increasingly valuable.”  (http://academicearth.org/about)