Here are some more sources of free b-roll that I have used lately.
The International Federation of Red Cross and Red Crescent Societies has b-roll from their missions in Asia & Pacific, Africa, Americas, Europe & C. Asia and MENA. http://www.ifrc.org/en/news-and-media/newsroom/
The International Committee of the Red Cross has different video than above also highlighting their activities in Asia & Pacific, Africa, Europe & Americas and the Middle East. http://www.icrcvideonewsroom.org/content/embed.asp?ID=8b56617.5m1352245hn53914.26
The United Nations Offices of Drugs and Crimes has b-roll from around the world highlighting their anti-drug activities. http://www.unodc.org/unodc/video.html
Bing has a lot of product videos of their product being used on other products such as cell phones, I-Pads and computers. http://www.microsoft.com/presspass/presskits/bing/videoGallery.aspx#channel_contentListTop
Walmart has b-roll of their stores which often show merchandise. I got some good shots of television sets here. http://walmartstores.com/Video/?id=1525
For more b-roll sources and information, visit the B-roll category.