Free stock video
Free Stock Video has a number of free videos such as the two below. You have to register with them and log in. Then, when you hover over the category tab, you can find and download all sorts of categories and subcategories of videos.
Mixed stock videos (free and otherwise)
Each month aLunaBlue introduces four new free videos such as the one below. They charge for the rest of their videos. Collect all four videos each month. After one year you can have 48 videos in your library.
An example of one of their free videos is below.