I’ve had luck with ClipGrab as a video downloader. But it’s been a while since I’ve used it. For YouTube downloads, I just tend to Google for an online YouTube downloader.
Also, I oye that VLC will often just let you type the URL for a video site and will just play the video. I know it works for YouTube and Vimeo, at least. And I seem to remember it working for Dailymotion.