lately we found ourselves often in situations where internet speed is too slow to effectively use online videos for educational purposes. to avoid the frustration of not being able to use these online resources, we have found the following indispensable:

ClipGrab
an application which allows download from any URL, and complete format control.

PwnYouTube
this bookmarklet focusses on youtube content and allows encoding in HD720p MP4, HQ MP4 amongst others.

obviously if you use any of the above please respect authors copyrights and give credit.