MVGroup recently made headlines when it was shut down because of a gay mistake made by an anti piracy organization. The site is now back and is accepting new signups. It has 150000 members and has a huge selection of television documentaries from reputed broadcasters such as BBC and National Geographic.
Site Name: MVGroup
Signup URL: Click on the Register a new account link beneath the login box.
Description: Lots and lots of documentaries and other educational stuff. Forum based site.