Unlisted Videos is a website that lets you submit, search, and watch unlisted YouTube videos. Unlisted video URLs can be submitted without registration.
Some examples of unlisted videos:
Bomberman vs Candy Crush (cartoon on the mashed channel)
Avengers: Age of Ultron (teaser trailer) (by Marvel Entertainment)
Final Fantasy VII for PC - Announcement Trailer (by Square Enix UK)
League of Legends: The Basics (by League of Legends)
Google Self-Driving Car on City Streets (by Google)