The Library of Congress has over 300 free Movies, clips, commercials and documentaries, filmed from 1890 to 1999, through the National Screening Room collection.
The National Screening Room is a collection of films hosted by the Library of Congress USA. The collection lists records about America's past that are considered "culturally, historically, or aesthetically significant" and have been archived by the Library of Congress. Most of the videos are public, and available for streaming or download.
The available collection can be sorted by title, date, original and electronic format, geographical location and subject. There are currently 336 videos in the collection, and new ones are added every month.
In addition to this collection, the US Congress library also has other collections containing songs and videos. A list of these you can find here.
Get in National Screening Room collection here.