Here are some interesting sites that I found very useful:
Keen Talks – Watch interesting talks, lectures, debates, presentations and interviews.
Sprword.com – site with a mission to build a brighter future for the entire planet by seeking and spreading truth on a global level, especially with their documentary section.
OVGuide.com – ultimate video search engine and directory for streaming videos websites. Documentary sites are included.
SnagFilms – the world‘s most compelling documentaries, whether from established heavyweights or first-time filmmakers, available to the wide audience.
PBS Frontline – Credible, thoughtful reporting combined with powerful narrative, a good story well told: That is at the heart of FRONTLINE’s commitment to its viewers.
Documentary Films.NET – valuable resource to those with an interest in documentary films.
Box Office Mojo – all time box-office list of documentaries.
HBO Documentary Films – offers a full spectrum of stellar, non-fiction programming by acclaimed documentary filmmakers.
Radio Documentaries – Award winning radio documentaries from Ireland – all freely available to listen online or podcast.