SafariStand is an awesome plugin that adds all kinds of great features to Apple’s Safari browser, including a thumbnail-preview sidebar for all open tabs.
One of SafariStand’s lesser known features is the ability to easily save Flash video files. All you have to do is Command-Click on almost any Flash video file (flv), and select the download item in the contextual menu that appears. note: the video needs to be completely loaded before this feature becomes active.
Once downloaded you can play the flv files directly in QuickTime via the Perian Plugin, or you can convert them with tools like iSquint.
SafariStand, Perian, and iSquint are all free.
On a side-note to this, if there are video on YouTube that you like, you may want to grab them for your personal archive, as many companies are really starting to crack down on YouTube for hosting copyrighted material. Viacom recently demanded that 100,000+ clips be removed, including popular clips from MTV, VH1, Nickelodeon, Nick at Nite, Comedy Central and Paramount Pictures.