The BBC recently released a new on-line motion library containing thousands of BBC film clips. The clips are free to download(after registration) but they contain a BBC watermark. Obviously this can be removed if you chose to purchase the clip but they are great for animation reference! 
Corbis, Artbeats and Gettyimages also offer similar services.
http://www.bbcmotiongallery.com
http://creative.gettyimages.com/source/frontdoor/DefaultFilm.aspx?brandID=6
http://www.corbismotion.com/
http://www.artbeats.com/
Enjoy