Al Jazeera (youtube.com/user/AlJazeeraEnglish/videos). Al Jazeera can be translate to "The Island" and is a channel launched in 1996. It has since the launch become a worthy competitor to CNN, and their YouTube channel features several documentaries of high quality.
Foundation (foundation.bz). Foundation consists of several interviews with American entrepreneurs. Among others, the interviews include Elon Musk (founder of Tesla Motors, PayPal, SpaceX, SolarCity), the magician David Copperfield, Jack Dorsey (founder of Twitter), and the author/investor Tim Ferriss. The channel started only a few years ago by Kevin Rose, who founded Digg and is now working at Google. I promise you will learn something new from each interview. You can see a summary of the all here: Lessons learned from the Foundation interviews.
Update! I found another one, so this is now a top 6 list.
Reddit Documentaries. (reddit.com/r/documentaries). Reddit is a so called social news website where people can submit links to websites they like and other people can now vote on the links. One of the sections of Reddit is "documentaries" where people can submit links to documentaries they have found.
...and another one.
Vice. Vice is an international magazine focused on arts, culture, and news topics. Vice News broadcasts documentaries about the world's most important, current topics. They have two good youtube-channels: