As Kaimax said, torrents from trusted sites are, well, trustworthy. Really, you have the same chance of getting a virus from a random video uploaded to Mediafire as you do a random torrent.
Anyways, to answer your question, there are some download add-ons for Firefox (and probably other browsers, too) that allow you to download a video stream from a website. I don't know any names unfortunately, but if you search the add-ons for the browser you use, you will hopefully find something.
Also, you can request a video in the Request section or check out User Uploads. Something you want might just be there.