The best way i find is to use safari. Go into the page with the video, open the Activity window (Window-Activity) and the download window (Window-Download). In the Activity window find the video file. (If it's there - which it's not always - it will be the really big file, prob the only one in mb...). Click on it, copy it (apple-c), select downloads window & paste (apple-v). It should start downloading it and work.
This doesn't work for alot of websites but i know it works for quite a few anyway. youtube being one. The other method (i've never used so... no idea how good it is) is a firefox Add-on called videodownloader 2.0 (the only link i could find quickly was https://addons.mozilla.org/firefox/2390/ which is for 1.1 but i know there's 2.0 out there since that's what i have) As i said, no idea how good it is though...
I just bought TubeSock tonight and it's excellent. I know you said you wanted a free one, but I just figured I'd chime in and say that TubeSock is well worth the $15 you pay for it.