If you use Firefox (and if not, what are you waiting for?) you are familiar with useful extensions such as Video Downloader, which allow you to save local copies of the videos you watch on websites such as Youtube or Vimeo. You can then watch these videos whenever you please.
But this doesn't account for those rare but possible times when you are not on your machine, or don't have access to a browser set up to your tastes. No extensions available.
That's where "KeepVid" comes in. Just enter your URL and it automatically extracts any video(s) found on that website and allows you to download in both FLV and MP4 formats. The MP4 would play on your Nokia, iPhone, or Blackberry too. The FLV file is a flash viewer file, and easily played using common video players – if you don't have VLC, get it pronto.
Here's a straightforward screenshot: