Truveo searches video content on the web by categories, channels and search terms.
Blinkx allows you to select a wide variety of categories, plus keyword searches.
Youtube searches the vast Youtube site for videos, with a range of complex filters. Youtube only searches the videos on the Youtube website, it does not search the web
When you run your search, you can select the filters at the top left. This will give you a range of options to filter your results, including: