There are several websites where you can find videos, You Tube being the most famous one, but not the only one.
An interesting tool to remove all ads around You Tube videos is Safe Share TV
Some videos may be gone when you need them or you may want to avoid an internet access failure from spoiling your plans.
You Tube Downloader is a free piece of software that you install in your computer and easily downloads You Tube videos
Save Vid is an online downloader if you do not want to install anything on your pc.
There is a variety of other tools to enhance You Tube videos in several different ways.
Tube chop allows you to choose a part of a longer video and save it.
Sometimes you need to add captions or subtitles
You tube itself
Blubbr.tv allows you to create quizzes based on videos
Here’s a tutorial
And here's an example based on a Blended Learning video.
If you want to edit your videos in order to create your own remixes, these are some options
Windows Live Movie Maker
Creaza Movie editor
Hope you have found some new tools to solve your video-related problems!