VideoCacheView lets you save web videos you've watched
If you watch a lot of web video on sites like YouTube, VideoCacheView is a great way to save your favorite clips for local viewing. It can find cached .flv files in your Firefox, Internet Explorer, Opera, and Chrome temp files. The latest version also supports adding a custom temp folder via the advanced options menu.
As you'd expect from a NirSoft app, command line arguments are supported. Launching VCV with /copyall and a destination directory will automatically dump all your cached video files to the specified folder in one shot (VideoCacheView.exe /copyall c:\SavedVideos).
It's not a downloader - VCV will only catch videos that have fully loaded in your browser. You'll also need an .flv capable application to watch your videos, like Gom Player or VLC.
VideoCacheView is available as a zipped, portable application or with an installer. It only takes up about 60kb of disk space, and is well worth a download.