I mentioned ScienceHack way back in August 2009 and I thought it deserved another post.
ScienceHack is a science video search engine that claims “every science video on ScienceHack is screened by a scientist to verify its accuracy and quality”.
ScienceHack also has videos categorized by science content areas such as physics, space, chemistry, etc. 
I did notice a few “dead links” or videos that were removed or are not embeddable. Despite this- I find ScienceHack to be a great site for locating science videos. It is also nice for viewing clips without the “noise” of YouTube comments, ads, etc.
See an embedded clip on Zebrafish Embryos Developing- just for fun.
Science for All 