I recently discovered this good Video downloader for Mac. It works without a problem, very simple to use.
A friendly downloader for YouTube and other sites
ClipGrab is a free downloader and converter for YouTube, Vimeo, Metacafe, Dailymotion and many other online video sites.
It converts downloaded videos to MPEG4, MP3 or other formats in just one easy step.
Visit and download at this website: http://clipgrab.org/
ClipGrab is free software, but only with donations can it remain free.